THE memorial service at my brother's school, Our Lady's High in Cumbernauld, was a quiet affair, with demure schoolchildren singing hymns and welcoming teachers clearly mourning his death themselves. They were showing us the theatre where he'd taught drama when the afternoon took on a surreal tone. "Come out and we'll show you the corridor," said one. We stepped through the door and it was like stepping into a different world, a tilted and treacherous world where the innocuous, institutional walls seemed shadowy and malevolent. Peter, my brother, had excused himself from his class and stepped out into this corridor. He crashed to the floor here, dead. Like a tree falling, they said. His body didn't bend.

I wanted to laugh. It was courtesy carried to an absurd degree, like that Monty Python sketch where the Mounties track a chap to his remote home to deliver a message. They burst into a jolly tune to tell him, "Your sister Rose is dead " Peter was dead too. We all stared in silence at the spot on the floor where he'd fallen. I wanted to howl with laughter. I wanted to howl.

In the days and weeks and months after a death, especially a sudden one, it's like living in a parallel universe where the world goes on as normal around you and nobody else seems to have noticed that everything has changed. The rules of normal behaviour seem irrelevant and you experience profound slippage between what you feel and what you are expected by society to do.

"It takes at least two years before you even begin to feel normal," says Dr Angharad Rudkin, a clinical psychologist who works with children and young people in Hampshire. "People say, You'll get over it. You'll recover soon.' But you don't ever recover. It grief is not an illness. You're adapting to huge change, having to live without this person in your life any more."

I never imagined I'd have to. My brother was woven into the history and geography of my life, part of who I was. He was a drama teacher by profession but was creative in various different arts simply because he loved them. He was a fine writer, photographer and musician and spent endless hours jamming with his best friends Paul Buchanan and Robert Bell of the indie-pop band Blue Nile, sometimes just on whatever kitchen implements came to hand - fish slices or potato mashers. "I was making a living doing something creative but we both knew he was at least as talented as I was," says Paul.

Peter lived on Glasgow's Byres Road and I can't go there without thinking about him, without expecting him to come round the next corner, as he did on one of the last times I saw him. I'd been at a talk on the serial killers, Leopold and Loeb. There was only one person I could discuss it with and I set off to look for him. I walked across University Avenue and down Lilybank and suddenly, as I turned into Byres Road, there he was, wearing the big tweed coat he'd inherited from our father and a look of pure delight to see me - as I had to see him.

It was my nephew Bob who phoned me on January 12 to tell me that he'd died. The school had called to say that Peter was ill. Bob didn't take it seriously at first. Peter was 54 and looked good. He was slim and bright-eyed and if his skin occasionally took on the smoker's sallowness, his creativity and humour counteracted it. "I had it in my head that it was something small or stupid, that he'd fainted or hadn't had enough sleep. It was a bit stressful and a bit weird. The taxi driver was a tube. He had one of those sat-nav systems that talk dirty. Go straight ahead and I'll give you head. It wasn't what you wanted at a time like that," says Bob.

His father was already dead when he got to the hospital, though the doctor didn't actually use that word when he broke the news. He said that Peter had had an attack. His heart had stopped beating and they'd tried to revive him at the school. Then the ambulance men had come and tried, for 50 minutes, to start his heart again. It was Bob who had to cut through the verbiage and say: "All right, so he's dead then?"

That was the beginning of a time of profound unease and social dislocation for all of us. In the tilted and treacherous world of grief, emotion constantly threatens to overflow the bounds of normality. It makes us question our place in the world. Peter's ex-wife, River City actress Barbara Rafferty, found her whole sense of herself as a physical being was under attack. "It's the shock. You're not right. You're kind of mad and you're not well. At the beginning I thought I was going to fall all the time," she says. "I drove down to Argyll one day with our son, Nick. The wind was howling. The waves were crashing in. A big moon was up. I said to him, It's seismic,what has happened."

What made things more difficult for her was that the world felt she wasn't entitled to her grief. She was the ex-wife, the one who had left after 27 years of marriage in an acrimonious parting. They met at drama school and had their first child, Amy, before they ever married. "We were supposed to get married on January 5 but we fell out," says Barbara. "That was why we had to get married in February. That was me and Peter. We really loved each other, but we couldn't live together."

"They were hilarious and also extremely hip," says Peter's friend Paul, the singer in Blue Nile. "They were three or four years older than me and seemed like adults who'd got it together. The first time I went up there for a meal the baby crawled across the table with his wee bare bum and they let him. Nobody even said anything. I thought, This is fabulous. I was just out of uni and the suburbs and I thought they were the bee's knees."

The marriage was always volatile and both found new loves afterwards - Barbara is now married to the actor Sean Scanlan - but their relationship had been a fundamental part of both their lives. Yet Barbara was being told she had no right to mourn. One of her best friends bought cards for their children but nothing for her. "I said, You know I've been in a terrible, terrible state about Peter, and she was almost like shrugging it off. I don't think people understood that I would feel it so much. Someone even said to me, You've done all your grieving for Peter when you split up'. Of course there was grief then but this is different. You feel like saying, for God's sake, you know nothing."

Grief is a monumental, ungovernable emotion. You can't absorb it, don't know what to do to rid yourself of it and it spills over in ways that are sometimes disturbing to the rest of society. The day Peter died, his 34-year-old daughter Amy went to the hospital with her two young sons to see her father's body. She couldn't go in at first, but broke down in the corridor, falling on to her knees and screaming. The staff came over to take control of the situation. "You're frightening your children," they told her.

Later she found the courage to go in and was crying, cuddling, whispering into his ear, when a priest came into the room and started talking without introducing himself (Peter taught at a Catholic school, but was a staunch non-believer himself). "I wanted to shout at him, What the f*** are you doing, standing here talking to me? Can't you see I'm busy? I felt I had this really cheeky look on my face," says Amy, though of course she talked politely to him, as convention required. The strangeness of her new world, this world of grief and loss so at odds with the normal demands of society, affected Amy and her brothers Nick and Bob in ways that sometimes seemed wildly inappropriate. Every sensation was magnified. One day they had a planning meeting with one of the funeral directors. Bob was in one room lying on the floor sobbing, while Amy and Nick were cracking jokes and laughing in the other. Bob had broken down because he'd been asked his father's address and felt he'd just given it glibly.

Nick found laughing the biggest comfort. "We were cracking jokes the whole time," he remembers. "That really amazed me. I always thought I'd be really angry, lashing out at people, but it's a different feeling when it actually happens. It just wasn't like that. It was constant jokes. I think we were trying to reaffirm being alive. Amy and Bob and I got taken to a wee room in the funeral parlour and they were saying, This is what we charge for the use of the lounge, and we were joking that Dad would be propped up in a chair. I was wondering if the guy was thinking we were being glib."

"That funeral director will have seen it a hundred times before," says Dr Angharad Rudkin. "When my dad died the funeral director came over and said, We'll get him dressed up in his favourite outfit. What is that? We said it was his Superman outfit. We fell into absolute giggles. The funeral director sat there with a really stony face while we couldn't control ourselves. It's great if you're with people who share your sense of humour and accept that it's a way of coping."

In the past, society would have found such behaviour unacceptable. You walked and talked quietly in the face of death, dressed soberly in black, and drew your curtains shut. The Victorians fetishised grief, building huge mausoleums to their dead, wearing black crepe for set periods of mourning, weaving the dead person's hair into miniature pictures of tombstones and weeping willows that were then set into brooches. But the 20th century brought the first world war and a flu epidemic, then the second world war. It would have been unseemly to make an ostentatious display of grief when so many were being lost. And it would have got in the way of war.

Grief is probably the most powerful - and potentially the most destabilising - emotion in society. When channelled into action it can be totally subversive, undermining the accepted hierarchies. "Every society seems to want to regulate the emotions of mourners. They don't want to just leave it without rules," says Professor Tony Walter, director of the MSc course in Death and Society at the University of Bath. "The passion, the emotion of grief is so potentially powerful that all ruling establishments have tried to control it. If Princess Diana's funeral service had been not in 1997 but in the middle ages, and if at the end of his speech Earl Spencer had raised his fist and said, Out with the Windsors and in with the Spencers, the power of the emotion not only inside but outside Westminster Abbey was so powerful that you could easily have had a change of king and queen."

My brother's funeral was a day of ferocious emotion which we reached after days of making decisions that seemed momentous. Every choice was weighted with significance because we wanted it to be the right one for Peter - the music, the speakers, the food. He was a quirky and original person and the traditional hymns and sausage rolls just wouldn't do. We started with 1960s drugs anthem, White Rabbit, which would have been even better if it had been as loud as he used to play it. The service was in Craigton Crematorium, where he used to play as a child. He was fearless, always exploring even though my mother had forbidden him to. He once brought flowers home for her, not realising they were funeral flowers.

The funeral fell on a grey day, the sky sodden with unshed moisture. The great black funeral vehicles glided in like a fleet of Mafia cars. "Coming into the crematorium there were all these people standing around. It was really artificial," says Peter's son Nick. "I looked at them and they were looking at us. Nobody knew what to do. I was thinking, Will I stick my finger up at them? I just did it. My friend said that everybody laughed - the release of tension was unbelievable."

Funerals are inevitably tense because no-one is quite sure how to behave; where they fit. They are formal events with their own invisible pecking order. In Victorian times people were expected to mourn for set periods according to their loss - three months for a baby, nine for a grandparent - and it's not so different now. My brother David lives in France and was entitled to just one day off because it was only his sibling who had died. But funerals are not just for the person's family. They are public events, a way for other people to show that he mattered. "A funeral is an opportunity for the community to pay its respects, to say that your grief is worth it," says Professor Walter.

There were so many people at Peter's funeral that many of them couldn't get into the main room and had to listen on loudspeakers outside. It was clear my brother mattered - to the bare-armed children from his school who formed a guard of honour in the cold; to his favourite barmaid; to the film producer, the composer and the schoolfriends who hadn't seen him for years but still came. "It was overwhelming, though I wanted to shout towards the eaves, Yeah, but I knew him best," says Paul Buchanan.

He probably did. They had been friends since their 20s. "After he died I was debating other aspects of my own emotions and other people's emotions towards me and I suddenly realised that I loved him," he says. "It was completely unequivocal, not obfuscated by sex or the demands that creep in. He had a moral core to him that was independent of any reward system. I walked along and sat outside the Ubiquitous Chip where he drank, and had a coffee and two cigarettes in his honour."

For Barbara, Peter's ex-wife, none of it was unequivocal. She hadn't seen him for over a year yet she wanted to be part of his death, as she had been part of his life. In the underworld of grief that we were all inhabiting, there was no doubt about her suffering. She had lost him once; now he was gone forever and she had no way to make things right with him. Her grief was an absolute - uncontrollable, even with her husband. "Sean was fabulous," she says. "I was crying and breaking down and I said, I'm sorry. He said, If you weren't, I'd be upset. I'd be wondering, What kind of person are you?"

But in the everyday world with its rules, Barbara was a problem. Where was her place in all of this? Where was she to go? Her children would be travelling in a funeral car but was it right for her to be with them? Amy thought not. "I felt disloyal doing this to Mum but I thought it was quite important. She had made a decision not to be part of the marriage any more and it just would have felt wrong. She was my mum and she was a massive part of my dad's life but they hadn't spoken for quite a while when he died. It was divided loyalty. I felt I was being pulled in both directions."

Faced with the irrevocability of death such things should have seemed unimportant, but in a strange way they become more important. We try to ringfence death with routine, with bureaucracy and orders of service and whether we've got enough booze, but our anxiety keeps crackling through. Barbara was utterly relieved when my sister offered to take her in her car. "It was great when Mary said, Come with me. I would have felt really uncomfortable if she hadn't, awful. I'd have tiptoed in at the end and gone away early." Barbara bought massive flower arrangements for the vestibule at the crematorium, beautiful explosions of white roses, thistles and lilies. Nick thought it didn't matter about flowers when his father was dead, but it was the only way Barbara had of showing that she had loved Peter.

More than that, it was an offering, a way of bridging worlds, of communicating in some way with the person who was gone. In the great civilisations of the past people made careful provision for the person's journey after death. Egyptian tomb poppets, little mummiform dolls buried with the dead, were there to act as substitutes if the dead person was called upon to work in the next world. China's first Emperor, Qin Shihuangdi, had a vast army of terracotta soldiers, archers, horses and chariots to proclaim his power when he reached the afterworld.

Nowadays many of us are not sure an afterworld exists and our carefully chosen words and music are almost designed to pull the dead person back into our world. For me, that bridging of worlds was what the funeral was about. More than simply a way of taking a formal farewell, more than allowing the community to mourn for my brother, it was a way for all of us who loved him to break through the barrier of death and lay a last offering at his feet.

I wanted him to be there, hovering round the edges, quietly amazed at the number of people who had come to honour him. Some people felt his presence, but I felt only his absence. Then Paul Buchanan asked everyone to make a noise for Peter. It wasn't what you expect at a funeral but it felt right. Suddenly the whole place was resonating with the sound of clapping and stamping, even whistling. It was an extraordinary, serendipitous moment and if ever it were possible to reach the spirit of someone who's gone, then I'm sure that joyous, crazy, loving cacophony reached my brother.