Wreathed in a halo of menthol cigarette smoke, June Brown is giving me a guided tour of her palatial bungalow in Surrey while talking to her late husband, the actor Robert Arnold.

"I'm always telling him to stop moving things around - things just disappear. I blame him," explains the 86-year-old actor and national treasure, discovering a Harlan Coben thriller in a spare bedroom. "I definitely left that in my other bedroom," she says, scratching her head in puzzlement. Does she often talk to Robert? "Bob, darling," she corrects me. "Oh, all the time because he's always with us," she replies airily. "He's here in this room."

He's actually with us now? "Of course. He's in there," she says, indicating an elegant cabinet in a corner of the comfortable, tastefully furnished sitting room before sparking up another Superking.

"You lift up the lid and he's inside." she reveals. "Or rather his ashes are."

All this may sound delightfully dotty, or even Dotty, for Brown is, of course, a soap-opera legend after playing EastEnders' chain-smoking washerwoman Dot Cotton - now Branning - for more than a quarter of a century. Indeed, she became the soothsayer of the spin driers when she was 58 years old, taking only four years off in the mid-nineties to do some stage work, including a critically acclaimed foray on to the Edinburgh Fringe in 1993.

More recently, she departed Albert Square for eight months, in January, to do other work and complete the first part of her remarkably honest autobiography, Before The Year Dot, in which she reveals a life that has been touched by great happiness, romantic love affairs, profound heartache and desperate family tragedies.

Her baby brother lived for 16 days. Her beloved older sister, Marise, known as Micie, died aged eight. Her first husband, the actor Johnny Garley, committed suicide after seven years of marriage. Her second child, Chloe, was born prematurely and, in a cruel twist of fate mirroring the death of Brown's brother, lived for only 16 days. After almost 45 years of marriage, her husband Bob, the father of her six children, died in 2003 after suffering for three anguished years from Lewy body dementia, which is associated with Alzheimer's and Parkinson's diseases.

All of which makes the many dramas and disasters of her alter ego Dot pale into insignificance.

"Joy and woe," sighs Brown, a devout Christian and supporter of the Conservative Party, who was appointed an MBE for services to charity and drama in 2008. "Joy and woe are woven fine/ A clothing for the soul divine," she continues, quoting William Blake's Auguries Of Innocence, one of two epigraphs in her memoir, which is a beguiling mix of innocence and experience, as well as being extremely well written, with all the stylish economy she brings to her acting.

The second epigraph is a three-line quotation from a personal poem, written for her in 1948 by one of her lovers, the Glaswegian playwright James Law Forsyth, who showered her with passionate verses. (The day they made love for the first and last time was an experience that left her "utterly cold, it was as if a feather was touching me," she confides. Indeed, she writes that had she continued with their illicit, unsatisfactory affair she would have felt as if she were a prostitute.)

"You know," she confesses, "I never had sex with any man unless I was in love." Truly, madly, deeply? "Definitely. I was always in love, constantly. With James, though, I'd only placed an arm around his shoulders for a photograph and he immediately thought we were in love. Poor, deluded man - his wife was pregnant at the time. We were close for a while; I'd become obsessed with his plays when I was at the Old Vic. But, yes, I couldn't exist without being in love, because it was sharing."

Was she a naughty girl? "Not like Princess Diana - now she was naughty!" she exclaims, adopting a gossipy stage whisper worthy of Dot at her most judgmental. "But I did fall in love a lot. I have been very honest in the book except I don't write about physical details. No way would I do that, apart from dear James, who was like a feather. The sex was terribly boring," she says, confiding a detail unsuitable for a family newspaper before inhaling another lungful of nicotine. (She has been addicted to smoking since she was 16 and claims her last blood test revealed her blood was nicotine-coloured.)

"I didn't want my book to be soapy - maybe it's my vanity but I think I can write better than that. I still feel I haven't measured up to my own standards. All is vanity," she murmurs. "I'm a perfectionist - but as someone once said, 'What else is there to be?'"

The raspy-voiced Brown is a consummate actor. Classically trained, she appeared on stage with Alec Guinness, John Gielgud and Peggy Ashcroft. She played Lady Macbeth and starred in many Shakespeare plays, but never got to play Cleopatra in Antony And Cleopatra. It's one of her few regrets. She was, though, the first soap star in 20 years to be nominated for a Bafta for best actress since Jean Alexander was shortlisted for her portrayal of Hilda Ogden in Coronation Street. The 2009 nomination - in my opinion, she was robbed - was for a heartbreaking episode of EastEnders devoted entirely to a melancholy monologue by Dot, brilliantly performed by Brown

So it's safe to say the eccentricity and dottiness that have become part of the Brown persona over the years are carefully honed. I interviewed her on the set of EastEnders just before she left in 1993. She kept saying: "Ooh, I've lost me thread," thus avoiding answering any probing questions. Today, she tells me I must beware of her tendency to go off on tangents. Her mind is always working, she says, and she never stops talking. When she had her tonsils out in the Royal Naval Hospital in Newton Mearns, near Glasgow - she was in the Women's Royal Naval Service (WRNS) during the Second World War - she talked to the surgeon throughout the operation.

Pin-thin, she says, "I've lost so much weight writing this book. I didn't have time to eat. I look like one of those starving children with a distended stomach. I feel like a knackered horse. Don't tell anyone." Her youngest daughter Naomi gives her a print-out of her author tour. "Am I on Piers Morgan or Desert Island Discs?" she asks. No, she's told, it's Graham Norton, Loose Women and Radio London. "Oh well, it ain't begun until the fat lady sings. I might be dead by the time it's over," she laughs.

I tell her there's to be no talk of dying. We await the second volume of her memoirs with bated breath, since Before The Year Dot ends with a brief chapter about her meeting and marrying Bob - who never told her he loved her so she stopped telling him she loved him - and having six children in seven years: Louise, Sophie, William, Chloe and Naomi, whose ages range from 54 to 47, and baby daughter, Chloe, who died. She and Bob separated for a while, then work dried up until, at the age of 58, she was offered a three-month contract to join EastEnders. "The year before I was offered the part was my worst ever. Things were getting desperate," she remembers.

But all of this is for her next book. "I had an affair when I was married to Bob, you know," she confides. "Should I write about it? He's dead so I suppose I can."

She points to a photograph on the wall. "That's me and Bob in The Lion In Winter - Bob was handsome, strong and athletic," she says. She was a great beauty, too, with enormous dark eyes and exquisite bone structure. The actor Nigel Hawthorne wrote that she was the most beautiful actress he had ever seen. Did she know she was beautiful? "Yes, I was quite beautiful, despite the teenage spots for which the only remedy was layers of Max Factor Pan-Cake."

Born in Suffolk to Harry Brown, a wealthy businessman who lost most of his money in the war, Brown was the second of five children. She grew up and was educated in Ipswich. Her mother, Louisa, who she believes loved her the least of her siblings, was a milliner. Brown is a "mongrel" - her paternal grandfather came from Scotland and her grandmother was supposedly of Italian stock. When she appeared on BBC One's Who Do You Think You Are?, she discovered that one of her great-great-great grandfathers, a Sephardic Jew, was a famous bare-knuckle fighter in the East End of London. Another ancestor was a renowned French rabbi. Brown was academic and wanted to be a biologist but her father said it would be a waste of money as she would only marry. When she was 40, she decided to study for A-level biology and perhaps train to become a doctor - "with five small children!" - but didn't finish the course.

She was 16 when she noticed that the fate line on her right palm had a distinct break at the age of 30 and ran on parallel tracks. A palmist told her something would happen then that would change her life.

"Of course, the extreme sorrow to come was Johnny's death - he gassed himself using the coins I had left him for the gas meter. He'd had an affair with another actress, Maggie W I call her, although I was the first to be unfaithful.

"I had an afternoon of sin with an actor I was working with at the Mercury Theatre in London, but it was only a fling. When you're acting you are in love with someone, it's very hard not to think you are. Johnny felt so guilty.

"But, in fact, my life was changed twice by death." She is referring to Micie's death from meningitis.

She writes: "The loss of her affected my whole character and shaped the way I behaved for a long time. In particular, it influenced my expectations of men. Too dependent, I found it impossible to be happy alone. I was constantly in and out of love, always looking for the kind of caring that Micie had given me - the wholehearted acceptance of me just as I was. I kept looking for the friend I had lost."

Today, however, she's happy on her own. "I've had to learn how to be." Nonetheless, after 10 years of widowhood - she has six grandchildren - she'd still like to share thoughts, meals, laughter, theatre visits, problems, house repairs with someone. "Not a husband nor a lover do I want. Just a compatible companion."

Her first love was Ralph Latimer, a Belgian. She was 14 when she fell head over heels for him and he became one of the family. They wrote to each other, then there was silence for three years during the war years after he was called up into the secret service. Nonetheless, she waited for him. "He broke my heart - the memories of that are the most painful of my life," she says. Comforted by his friend Jean Palissau, a handsome young French lieutenant in the British Army, she lost her virginity. She never saw nor heard from Ralph or Jean again.

After joining up at 17, she did her basic training in the WRNS in Scotland, at Balloch, and has "no desire to return to the bonnie banks of Loch Lomond - it would bring back too many unpleasant memories. Scrubbing floors at five in the morning! I simply wasn't used to it."

Brown had a good war, though. "It's dreadful to say but I never lost anyone. I had so much fun."

She hoped to train as an aircraft mechanic but became a cinema operator and had the horrific experience of showing the newsreel films that came out of Belsen after the war because she was the only projectionist in Ardentinny in Argyll. "It was extremely shocking for a girl of 18. We were a very innocent generation," she says.

She was posted to south-east England, then back to Scotland where she fell in love with dashing Sub-lieutenant Colin Parsey - they became lovers and she got a weekend pass to visit him in Troon, staying as his wife in a small hotel. "That was quite a common occurrence during the war as you might not see the other person for some time. There was no certainty during the war." She also discovered the joys of acting in the WRNS and, after the war, won a place at the Old Vic Theatre School in London, "a heavenly time of my life".

Soon, she was in love again - there was al fresco sex in a field in Colchester, Essex, with the actor Edward Jewesbury when she was 21. She met another actor, a Scot she calls only Donald in her memoir. They fell for each other at drama school, but he suffered from crippling bouts of schizophrenia. She visited him in an Edinburgh psychiatric hospital and stayed with his mother, who had been desperate for them to marry. Instead, Brown married Johnny Garley.

"I found that companionship I'd been looking for with him for a while - he was a great sharer and he did look after me and I looked after him, so I was very happy in my marriage, and unhappy when it ended."

A friend, a clairvoyant who lives in Paisley, has told her she'll live to be 100. "I don't want to," she insists. "Not if I'm unable to work. However, I've planned my funeral. I want to be buried at sea. The Britannia Shipping Company drops you off round the Isle of Wight. I'll be in a nice white nightie and they wrap you in a balsa wood coffin and weight it. I must get it ordered."

As we part, I ask her why Dot, once so bitter and twisted, seems to have morphed into Mother Teresa in EastEnders of late. "I can say nothing. I'm under contract," she replies, dragging on the last of a chain of cigarettes. "However, I do still try to slip those bits of her back in, but you can't go against the writing."

Nonetheless, Dot's still an icon.

"Icon? Acorn more like," she cackles in Dot's familiar cigarette-scarred basso profondo. n

Before The Year Dot by June Brown is published by Simon & Schuster, priced £20. Brown will discuss the book and sign copies at Waterstones, Sauchiehall Street, Glasgow, at 6.30pm on November 19. Call 0141 332 9105.