'The whole family are proud of what I do,' says Chris Spencer, contemplating whether he wants to take a bite of one of the Scottish National Galleries' famed scones (he doesn't like scones). His mum has just arrived on the train from Newcastle to say hello to her son – who finds himself in the unexpected position of being commissioned to create a bespoke piece of art for the SNGMA's Cut and Paste exhibition – but he's kindly taken time out of the reunion to finish our chat.

'Aside from my children, who are really embarrassed,' continues the Birmingham-based father of three daughters. 'One's a teenager, who doesn't want to have anything to do with it, middle daughter's kind of indifferent, and youngest daughter, who is five, doesn't really get what's happening. She keeps saying, "Dad, when are you going to finish Cold War Steve? Come and play!" I'm like, I've been commissioned by the Scottish National Gallery, leave me alone … '

When he speaks, it's with the dry humour and self-deprecating manner of a stand-up comedian, although Spencer isn't a star as much as a viral sensation. He 'is' Cold War Steve, creator of the Twitter account of the same name, whose bleakly amusing cut 'n' paste collages of the actor Steve McFadden (aka Eastenders' Phil Mitchell) and various principal characters of the current political landscape have brought him internet fame. He has, at current count, more than 200,000 Twitter followers, and his work has appeared in the Guardian, the Big Issue and – most memorably – on the cover of the international edition of Time magazine.

Given that her dad is an online sensation, it seems odd that his eldest child isn't fussed. 'You'd think!' he smiles. 'When I first started I got about a thousand followers in a couple of weeks, and she was like, "it's hardly Justin Bieber is it?" But it's fine … keeps me grounded.' A little over three years after McFadden's Cold War – as the account was then – first appeared, how has he adjusted to its escalating success? 'I don't take it for granted,' he says. 'It's come so late, really. I went to art college but didn't go to university; just worked mundane factory jobs to make money. So this all came about at a late point, and it's mind-blowing, but I don't take any of it for granted.'

https://t.co/tuv6Vb1nmu

— Cold War Steve (@Coldwar_Steve) August 31, 2019

When Cold War Steve began to take off, Spencer was a probation officer, and technically still is. 'It's quite an intense, stressful job,' he says. 'As this picked up more and more, and I started to do prints and interviews and exhibition work, (his employers) were brilliant, they gave me a twelve-month career break. That's what I'm on now, and hopefully by the end of it I'll be able to make a full time living from this … my work is my own views, not the views of those I work for etc etc. I didn't reveal who I was until last year, but it wasn't to be mysterious or aloof like Banksy. It was just that I didn't want to get the sack for doing this!'

Like the Time cover, the SNGMA commission – a large piece on the railing outside Modern Two, featuring a bright seaside cornucopia of C-list British celebrities and politicos – is a dream come unfeasibly true for him. 'I never thought I'd be exhibiting in a place like this,' he says, noting that 'I've been to Edinburgh loads. I thought my chance to get something in an art gallery had long gone after college.' He studied art in Nuneaton, where his studies were superseded by the band he joined; whose music wasn't as vitally important to him as the collages he made for their flyers; until all of it paled next to the simple graft of making a living.

'I think the gallery didn't want the piece to be too political,' he says, returning to the reason he's here today, 'but that was fine, it gave me an opportunity to do something completely opposite from what I normally do. My pieces are always dystopian, they're all linked to Brexit in one way or another, but it's such a beautiful building, such beautiful grounds. I didn't want to sully it with some horrible picture of Rees-Mogg or Farage. I wanted to reflect modern Britain, and all the diversity and creativity that it has. It's a picture of hope, I suppose.

'I took the lead from the Martin Creed piece which is on the other building, on Modern One, Everything is Going to be Alright. Now, he wasn't necessarily saying that everything is going to be alright and nor am I, really, but that was the starting point; we've still got diverse, creative people in the country, so there is some hope there. The piece is called Harold, the Ghost of Lost Futures. It sounds a bit pretentious, but Harold is (elderly Neighbours soap character) Harold Bishop at the back, parping on his tuba, an icon from my '80s childhood. He's signalling that my children might not have such a colourful, diverse future if things go the way they're going, so it's tinged with a darker message.'

Creed isn't the only Scottish artist referenced; David Shrigley's Partick Thistle mascot Kingsley also appears. 'Yeah, I had to get him in,' smiles Spencer. 'Shrigley's great, and I think we have a similar sense of dark humour. Kingsley was the missing piece, actually. I did it all, but something was missing … I put him in the back, then in the sea, then I thought no – front and centre, blazing out! With his slightly aggressive face.'

Given that all of his works in some way reference Brexit, it's pleasing to see Spencer step out of his comfort zone, and yet still create something which is thoroughly Cold War Steve. 'Doing this was just a way of dealing with my anguish about Brexit,' he says of the Twitter account, 'because it's something that's causing me a lot of anguish. This is a form of therapy, really; for me to do something that's fighting against it, if I can. Will it make a difference? Probably not, but the following I've got, they're of a similar mind to me. I think we all get some comfort in laughing about it and sending it up.'

We've been joined by Spencer's manager Carl Gosling, who manages the Social in London, and who has been helping steer Spencer's career since he held a small exhibition at the venue a year ago. 'The one word as to what's happening next for Chris is "America",' says Gosling. 'Weirdly there seem to be quite a lot of people interested there – when we do a mailout, this is really boring, but twenty percent of the opens we track are from America.'

'I don't know if they're expats or if they came through Trump, because everything with Trump in it gets a decent following in America,' says Spencer, who has to catch up with his mum before transatlantic domination can happen. 'It's really sweet, they read through the comments and Google the characters; one person in Washington was looking up Adrian Chiles, another was finding out about Harold Shipman. What I do is British humour, I know, but the hope is to have a decent crack at it. It's there for the taking, with the primary connection next year.' Whether he proves to be Monty Python or Benny Hill when he gets there, his is the comedy which has defined this moment.

Cut and Paste: 400 Years of Collage is at the Scottish National Gallery of Modern Art (Modern Two), Edinburgh, until Sun 27 Oct.