BARELY have I plonked myself down into a chair next to Arabella Weir, than we're off and running. Most interviewees need time to warm up, but I'm still fishing out a notebook when – above the cacophony of noise in an upmarket Glasgow hair salon – she launches into a story about her "horrible Dunfermline granny" who had "something negative to say about everyone in the world".

If there had been a seatbelt, I would have buckled it at this point. Over the next hour, the comedian and writer – who coined the catchphrase "Does my bum look big in this?" for hit BBC sketch series The Fast Show – fires off a volley of witty one-liners alongside colourful anecdotes about childhood holidays in Scotland, motherhood, bereavement and fractured family ties.

There are moments where it feels like I'm staring into her soul. "My mother and I always had a tricky relationship," Weir tells me at one stage. "I was very fond of her, but she was by no stretch of the imagination 'a mother'. She was aggressive and withering."

She equally reflects on how the first seeds of negative body image took root at a formative age, portraying a child who felt like a constant source of disappointment to her parents. "They never stopped going on about how fat I was from when I was little. I think my parents were embarrassed that I was short and plump. I look at pictures now and think: 'Christ, I'm nothing like as fat as they made me feel.' I thought I was enormous."

With such unflinching candour, it is easy to get side-tracked from the task at hand: talking about her role in BBC Scotland sitcom Two Doors Down. The show returns for a second six-part series on Monday with Weir as Beth Baird, the ballast of neighbourly relations in fictional Latimer Crescent.

When we meet, the 58-year-old actor has newly wrapped filming and cheerily describes being reunited with cast-mates Elaine C Smith, Jonathan Watson, Alex Norton, Sharon Rooney and Doon Mackichan as "a bit like a second date, but not quite as terrifying".

The dynamic is reminiscent of her time working on The Fast Show in the mid-1990s. Charlie Higson, she says, would describe himself and co-creator Paul Whitehouse as the mum and dad of "one big f*****-up family". To which Weir would quip: "But just as f***** up as the kids."

Two Doors Down has a similar happy yet dysfunctional family vibe among its cast. "But in our group, there is no one clear mum and dad," she clarifies. "We are either all bickering children or we are all the parents depending on the mood."

The latest series was filmed at BBC Scotland's studios in Dumbarton and on location around Glasgow. "They are a lot more scenes with us all together," she says. "I think they thought quite rightly that those are the ones that work best. If you take Till Death Do Us Part, Porridge, any of the great sitcoms – it is when everyone is in the room that it is the most fun to watch."

Weir was particularly fond of working alongside Smith, best known for playing long suffering Mary Doll in Rab C Nesbitt, and Mackichan, who previously starred in Channel 4's Smack the Pony.

"There is some very good comedy stuff with Elaine and Doon's characters driving it," she says. "Elaine is a much bigger presence [in this series] than she was before. That is probably because her character is the best vessel for the greatest jokes that are so awful that no-one else can say them.

"She has got a number of fantastic gags. I always think of Elaine's character as slightly the Mrs Slocombe [from Are You Being Served?], this extreme character who can say the things an ordinary person can't. If Beth made half her jokes, you would think that she had gone completely mad …"

The lack of older women gracing our television screens is an enduring issue. Only last month Ofcom chief executive Sharon White said the BBC is "falling short" on its obligations in this area. In that context, Two Doors Down is arguably a welcome breath of fresh air. "It was Elaine who pointed it out: how often so you get three women over 50 in a show?" says Weir.

The opening episode sees the long-suffering Beth railroaded into hosting a barbecue, stoking the flames for some hilarious Machiavellian shenanigans as her neighbours gather to indulge in their favourite pastime: one-upmanship.

How do Weir's real-life neighbourly relations compare to that of her on-screen alter ego? "I'm very fortunate in that I'm good, close friends with at least eight of my neighbours," she says. "That is very unusual in London and probably most urban areas."

She describes herself as "an extremely good but also a little bit of a nosy neighbour". Define nosy, Arabella? "I might be fully aware of what everyone does. Although not quite a curtain twitcher, I am part of the local Neighbourhood Watch."

She makes a mock horrified face. "You do sometimes think: 'God, what have I become?'" Turning into her mother? Weir gives a fervent shake of the head. "No! My mother couldn't give a flying f*** who was living next door. She was like: 'It's nothing to do with me …'

"My mum was an only child and very insular whereas I'm like: 'I don't want my kids walking down that street without me knowing who is around and whether they are safe.'"

As it transpires, Weir even has a nickname. "My very good friend – who is also my neighbour – says I'm the Neighbourhood Witch, which is a play on Neighbourhood Watch. She bought me a sign for my window that says: 'The Neighbourhood Witch lives here.'"

Weir, also known for TV roles in Skins, Doctor Who and Drifters, lives in north London "along with all the other Scottish actors". She says: "There is quite a lot of us in our square mile: Peter Capaldi, James McAvoy, Sylvester McCoy and until recently David Tennant ... It is nice knowing there are other Scots around.

"My parents moved to north London when everyone of their generation moved to south London because it was an hour closer to Scotland. Not sentimentally, they were just thinking of the journey. My dad would say: 'I'm not spending an extra hour in traffic if I don't have to.'"

Her late father Michael, a former British ambassador in Cairo, was a diplomat and his foreign postings became a way of life. Weir was born in San Francisco and grew up mainly in London but also spent time in Bahrain; nonetheless she has always remained proud of her Scottish roots. Her father came from Dunfermline, while her late mother Alison was born in Easter Ross and grew up in Melrose.

"When we lived abroad we never went back to London – it was always Scotland," she says. "Culturally, I regard myself as Scottish. My parents behaved like they were Scots. There was no regarding London as home; Scotland was home. We would come back and have horrible holidays with the horrible granny in Dunfermline."

In the summer of 1965 her father bought a VW camper van and packed the family up – including Weir's two elder brothers and her younger sister – to make the 600-mile journey north from their Camden home for a holiday in Plockton.

"We drove to Scotland for what seemed like hours because it didn't go very fast," Weir recalls. "There was four of us in the back including my sister in a baby carrier.

"We would read books by the light of the car behind all the way up. I would tell Dad: 'You've got to go in front of another car so we can read.' We would sing songs too. I saw inside a camper van the other day and thought: 'How on earth did six people fit in that?'"

Weir remembers stopping off en route to visit her maternal grandmother in Melrose. "Because there was so many of us, when we went to my granny's house, she couldn't put us all up and we had to stay in the camping ground," she says.

An amused flicker crosses her face. "My parents would leave us in the camper van and would go to sleep at Granny's. Imagine people doing that now? Leaving their kids half a mile away. But, of course, nothing ever happened."

Not all of Weir's childhood memories are quite so warm and fuzzy, particularly her troubled relationship with her mother. "She was extremely unhappy and I suppose, looking back, she was depressed," says Weir, recalling how her mother would nit-pick every tiny detail.

"'Does my mum look big in this?' didn't come out of nowhere. My mother was always on about how fat I was, that I may think I was great but I wasn't, so-and-so is better than me, and why can't I be more like them …"

After her parents split when Weir was 11, things deteriorated further. "I was very combative and asking: 'Where's Dad? Why aren't we living with him? What is going on?' and she wasn't admitting anything. It was just: 'Don't ask', 'shut up' and 'I don't want to talk about this'.

"Her then boyfriend was around all the time and I was thinking: 'Who the f*** is this?' My mother and I always had a pretty tricky relationship and I said as much at her funeral."

Over the years, Weir has attempted to make sense of why they perpetually knocked heads. "As I got older I said to her: 'Do you think you were jealous of me?' and she said: 'Yes, I think I was very jealous of you.' Right to her dying day she was capable of being incredibly unpleasant and withering.

"With my kids as well, she would try to pit them against each other. I went mental and said: 'If you try to do to them what you did to me, I will kill you.' It was a very aggressive relationship."

It is only now with time and distance – not to mention therapy – that Weir says she has been able to gain much-needed understanding and find a degree of closure. "I realise now she was projecting. My mother was incredibly intelligent and highly educated, but she was expected to do canapes and wear a nice dress. I think she was very frustrated and had thwarted ambitions. She eventually became a teacher and was very happy doing that."

Curiously, however, Weir exudes an odd sense of gratitude. "My sister sometimes says to me: 'Where would you be if Mum hadn't been so horrible to you?' It may have been the grit in the oyster. I wouldn't wish it on anyone because she was very aggressive and undermining.

"I thought: 'I will either be the disappointment she sees me as or I will try something else.' I never set out to be successful. It was just that, and this is quite sad, but I didn't want to be like her. She was a spur to me in that way."

Nor was it all bad, she insists. "My mother had a fantastic sense of humour, so it sounds like it was unmitigated hell and it wasn't: she was simply not equipped to be a mum."

Their often toxic relationship shaped Weir's approach when it came to raising her own children Isabella, 18, and Archie, 17. "I once said to my mother: 'Every single thing you did, I'm going to do the opposite.' To her credit, she said: 'You will probably be all right then.'"

Her father Sir Michael Weir, who died 10 years ago, was academically gifted. The dux of Dunfermline High, he won a scholarship to Edinburgh University, but then the Second World War intervened.

"He was posted to the Middle East and, as it came out later in his life, he trained as a spy for the RAF. After the war, they said they would send him to Oxford so he could join the Foreign Office. He started out as a diplomat and ended his career as an ambassador."

There is warmth in her voice, yet Weir would be the first to admit that their father-daughter relationship was not without its foibles either. "My dad – and this is a man with an incredible brain – did actually say: 'I can't help loving you more if you are thin.' My parents didn't think there was anything wrong with saying that. They thought they were incentivising me to be thinner. They wanted what everyone wants: a thin, pretty girl."

Still, she reasons, without this we would arguably never have had "Does my bum look big in this?", which the Oxford Dictionary of Catchphrases credits as being coined by Weir. A fact she bullishly points out, before smiling: "I only say that so heatedly because any time anyone goes: 'Oh, that was already out there …' I say: 'No, it wasn't – that was my achievement.'"

Weir split from her husband Dr Jeremy Norton in 2013. She looks coy when asked whether she's dating anyone. "Sort of ..." There's a pause as Weir hums and haws. "I'm seeing my ex-husband which is slightly weird," she says, finally. "It's very difficult to shake off that connection, the ties that bind to the father of your children."

Weir was navigating a tumultuous period in her life when their relationship faltered. "My best friend died, my father died, my mother died, my stepmother died – everyone died," she says, simply.

"I split up with my husband at a very miserable time and that obviously made it more miserable. He wouldn't like to hear this, but I never thought I would cope. I really think parenting is unbelievably hard if you are doing it well. A lot of how happy I am now came from finding out that I could do it."

There is a twinkle in her eye, although Weir is reticent to put a label on their rekindled romance. "It is early days, but quite nice," she says. "I certainly don't fancy being naked in front of a new person. I don't want to do all that s***."

Given her past battles with body image, how content does Weir feel in her own skin these days? "Much more comfortable than I did," she says. "I wouldn't mind not having a spare tyre. The exchange for me, though, is that I'm not prepared to put myself through the minute-by-minute thinking that is required to make me thinner than I am.

"I want to go a party and have three glasses of wine or eat a plate of chips if I feel like it. I dare say I could be two stone thinner, but then I would have to be someone who never had pudding, wine or biscuits with my coffee and I couldn't live like that.

"Would I wear leggings? Yes. I would wear anything I liked. I suppose I'm more comfortable than I ever expected to be in my body and that is probably the best I can do."

Two Doors Down begins on BBC Two at 10pm on Monday. Thanks to Taylor Ferguson ( and Abode Glasgow (