Amanda Abbington on her West End show The Unfriend: “I’m very polite, unless I’m in the car on my own”

Amanda Abbington has always been terribly polite. Well, mostly. “Unless I’m in the car on my own and people don’t say thank you,” she says. “Then I'm really mouthy and nasty.” She’s not kidding. She once got so cross on the motorway that she actually followed someone in her car to a service station car park to tell him off. He was mortified, and she ended up buying him a coffee because she felt so bad about it.

“That's one of the most embarrassing things I've done,” she cringes. “From ‘why don't you say thank you?’ to ‘have a cappuccino on me’. I'm really sorry. Come and live in my house. Please have all my money.”

Her terminal courtesy is one of the reasons that her latest play, about to open at the Criterion on Piccadilly Circus, hits so deliciously. The Unfriend, the first play by Sherlock’s Steven Moffat and directed by Abbington’s co-star in that show, Mark Gatiss, is a farce-of-manners about an English couple, Debbie and Peter (Abbington and Reece Sheersmith), who meet a larger-than-life American woman (Frances Barber) on holiday.

Unable to be anything but horribly polite, they end up accidentally having her to stay – despite the fact that a cursory (but rather late in the day) Google reveals that she’s quite likely to be a serial killer. Slightly alarmingly, Abbington tells me that it’s based on an episode that actually happened to friends of Moffat and his wife, the TV producer Sue Vertue.

“Yes, Steven and Sue have really close friends called Debbie and Peter, that was their real names, and they did go on a cruise, and they befriended this American woman, and they swapped email addresses, and the woman rang them and said, I’m coming over. Before they agreed to it, they Googled her, and she’d killed three people in America and got off on a technicality,” she says. “So they were like, ‘Erm, would you mind not coming over?’”

Abbington is unfailingly polite in person, breezily disregarding it when I knock something over in her cosy but relatably chaotic sitting room – something belied by her occasionally lairy persona on Twitter. “Oh no…” she groans, when I bring it up, putting her face in her hands. “I have to do this thing now with my best friend. Whenever I get really angry, and I want to tweet something, I send it to her first and she’s like, ‘Absolutely not. No, you can’t. Just breathe, maybe sleep on it…’ – I just get really angry with people.”

To be fair, victims of her ire in recent weeks have mostly been the likes of George Santos (a “lying, nasty shitbox”) and Andrew Tate (“abject filth”), so, you know. She admits too that she didn’t deal particularly well with the social media backlash against her character Mary in Sherlock.

“She was such a divisive character, in terms of people loving her and hating her, and a lot of people got cross that she got in between John and Sherlock – and that I was in between Martin and Ben,” she says. “The blurring of reality and fiction was quite interesting and a credit to the show, but I defended myself quite angrily. Looking back now I think I would deal with it differently.”

She’s trying to be less outspoken these days but she’s exercised by the plight of women. “I see women in Iran and Afghanistan losing their rights, and in the US – that really upsets me. And I think that we’re not on such firm ground over here either; that [reduction of reproductive rights] could happen here, it’s a slippery slope,” she says.

“I had an abortion. It was an accident, [the pregnancy] wasn’t meant to happen. I was very young. But I couldn’t have looked after a child, there’s no way. And to have that taken away, especially from younger women, kids. It just doesn’t bear thinking about.”

She adds, “We have spent decades trying to be heard and trying to be taken seriously, and it’s just being eradicated, bit by bit.”

Abbington is also furious about the way she has to parent her daughter differently to her son. “She’s 14 now. I was walking with her in the summer; she wasn’t wearing anything revealing, just T-shirt and a pair of tracksuit bottoms, but she’s turning into a woman, and the amount of unwanted male attention that she got... And I was just thinking, this is how she’s now got to go through life, just fending that off, and being told that if she wears something, then she’s asking for it. Or not wearing her hair in a ponytail when she walks home because somebody could grab it. And it’s, you know, teaching her to walk with keys in her hands and things like that. It shouldn’t be like that.”

Women’s rights can be complex and dangerous territory – she issued a swift apology a couple of years ago after a remark about trans people that she then described as “ill-informed and incredibly hurtful”, but there are still sections of the internet that remain unforgiving. All she wants, she says now, is that women be given “the right to choose what they want to do with their bodies, to be who they want to be and feel safe; to feel like they can walk about the streets without feeling threatened all the time.”

She does charity work for women’s refuges, and says that “just wanting women to have safe spaces where they can go and be, and not worry about the threats, that’s all it is – I don’t think it’s a particularly, you know, inflammatory thing. We all need places where we can go and feel safe, everybody – it doesn’t matter who you are; women, trans women, trans men - everybody needs a safe space.”

Ultimately, she says, “I don’t want anybody to feel threatened or feel that they can’t go and be somewhere or do something, do what they want to do. I was bullied for a long time when I was a kid. I get that, I understand feeling alone and frightened. We just have to take a breath, and remember that we’re probably all on the same page.”

That bullying, she says, contributed to a crippling lack of self-esteem that she has battled against ever since. It was a group of girls, in high school, and the effect was exacerbated by “family members. I don’t even think it was intentional, but it would always be like, you know, ‘Oh, you’ve got a spot on your face’ just before going out. Just picking, in a kind of jokey way, which is what family members do, but they don’t realise it’s insidious. They just think they’re being funny. And then I found I just sort of picked people, partners, that did the same thing – unintentionally, but undermine me and just make me feel a little bit, you know, crap.”

It’s not entirely clear whether her former partner Martin Freeman, from whom she separated in February 2016 while they were still making Sherlock together, is included in this list (they have an amicable relationship and co-parent their two teenage kids), but either way, she says, “then I went into therapy, and I suddenly had an epiphany – ‘Oh, okay. I’m not actually a bad person.’ I had to do a lot of work on not everything being my fault.”

Lucky, then, that her fiancé, the former stunt performer Jonathan Goodwin, is also a qualified hypnotherapist, which she has found to be a bit of a miracle solution, despite being initially a bit sceptical.

“I had a little relapse a couple of weeks ago, and he did 45 minutes of hypnotherapy. It shifted something in me. He did it with my friend as well, and he’s worked with people who have phobias and people who have extreme anxiety, and they’ve rung him and said, you know, we’re going to recommend you to everyone.” Her daughter wasn’t convinced either, until Goodwin used the power of suggestion to make her hands stick together (he used to live with Derren Brown, which makes a lot of sense).

Goodwin, who greets me cheerfully when I arrive in their warm and inviting kitchen, is, she says, unendingly positive (“so annoying”) - an extraordinary feat of character considering that two months into their relationship his performance career was ended by a life-changing accident during rehearsals for a stunt in Atlanta. His injuries included a severed spinal cord, broken spine, shattered legs and third-degree burns. When she sped to his side, having received that terrible phone call, he gave her the option of leaving, saying he wouldn’t blame her.

“I was like, you being slightly lower in a wheelchair doesn’t make any difference, you’re still the person that I fell in love with,” she says. “And as if I’d leave you because of an accident. I’m not that person. I love you.”

Goodwin is “just so strong. He’s incredibly tenacious and hardworking and intrinsically happy,” she says. “He’s very good at putting things into perspective. He’s faced death twice in a very short space of time. He had the accident, then he went down to the operating theatre and they told him he had a 50-50 chance of surviving [the operation]. So he’s looked death in the face and now he’s like, ‘we sweat the small stuff too much.’”

Abbington feels a responsibility now, she says, to speak out for wheelchair users. “You suddenly realise how little they’re looked after, people with disabilities aren’t catered for worldwide. It’s really noticeable, just little things. We were in Budapest, where I was filming. and there was a wheelchair access toilet, but it was down a really steep, narrow flight of stairs. We were like, ummm…”

The couple live together in Hertfordshire in the home where Abbington has brought up her children – a rambling old house but fortunately not listed, so they were able to install a lift – and also have two extremely excitable small dogs, who she refers to affectionately as “dickheads”. She’s happier now than she’s been in a long time, she says – her days of “self-sabotage” due to anxiety seem to be behind her. When I leave, she gives me a lift to the station – as ever, unfailingly, terribly polite.

The Unfriend is at the Criterion Theatre to April 16; buy tickets here