MARK Thomas and I are doing what many middle-aged British men thrown together by circumstance would do at this time of year: we’re making small talk by chatting about our family holidays. Except I’ve gone one step further: I’m showing him photographs of a past trip. This isn’t as indulgently self-obsessed as it sounds. Let me explain.

In April 2005, my wife and I went to Cuba on holiday. Flying out from Heathrow, I noticed Mark Thomas in the row in front of us. The previous summer, the activist-comedian’s Edinburgh Fringe show’s revelations about Coca-Cola had left a deep impression on me (I haven’t knowingly bought a Coke product since) and I was desperate to tell him this. But, I thought, he’s heading off with his family and I can see that he’s got that big thick Nelson Mandela autobiography to read; leave him in peace. We got off the plane at Holguin in the east of the island; they stayed on to land in Havana in the west.

We spent the next week and a half driving up through Cuba, stopping off at different towns along the way. At times I kicked myself for not at least telling Thomas I’d liked his show. Then we arrived at the Hotel Moka in Las Terrazas, about an hour’s drive outside of Havana. And who did we see in the restaurant at breakfast?

In the years since, I’ve told this story to a number of friends (“You met Mark Thomas when he was on holiday in Cuba? Oh yeah? And was Billy Bragg carrying his luggage?”) and I’ve even reminded Thomas about it when we’ve crossed paths in August during the Edinburgh Festival. But this is the first time I’ve had the chance to dig out some of those Cuba holiday snaps and thrust them in his face. Remember this place, Mark?

“Yes, the eco lodge,” he says, looking at the picture. “The tree growing up through the middle of reception. I remember because it was my birthday while we were there. What year was it? I would have been 42, and I remember being there because my wife and kids had asked what I wanted to do for my birthday, and I said I wanted to do something I’ve never done before. And so I rode a horse for the first time ever. I thought it was great, but my bum hurt afterwards. And I’ve never been since.”

I also show him some photos of the natural pools in the river nearby, where tourists and locals swam together at weekends. I’m sure he must have gone there too as his wife, Jenny Landreth, writes an online swimming blog and last year published a book called Swimming London about the capital’s top 50 pools, lidos, lakes and rivers.

“Oh, bloody hell, I do remember going in one of those,” he says. “The first real holiday Jenny and I had together as a couple was in Portugal. We ended up about a mile from a place called Coimbra, up a mountain. There’s a place where two rivers meet and form a natural pool, at a monastery where the monks have put in a bit of concrete to slow the flow of the river in and out, and a diving board. Ever since then it became a tradition that you’d have to go and find a pool of cold water and jump into it when you’re on holiday.”

We haven’t hit on these reminiscences directly, of course. This being a conversation with Mark Thomas, there have already been plenty of political side-tracks and off-subject rambles along the way. Before I’ve even got the photo album out, he has taken a pot-shot at the Labour Party’s recent abstentions (“What is the point of having an opposition if you won’t oppose things? I think Labour have just given up the ghost”) and given the thumbs-up to Nicola Sturgeon’s explanation of why the SNP should weigh in on the fox-hunting vote (“Politically she’s right, but also tactically she’s absolutely right to remind Cameron that, actually, he has not got this huge majority – he scraped in”). There will be plenty more of this before we part.

The main subject at hand, however, is Thomas’s upcoming return to Edinburgh with his new show, Trespass. This time he will be pointing a finger at the private companies and city councils who want to take urban spaces away from the general public.

“One of the big motives for me is the idea that the place I live in is changing so quickly,” he explains. “I am obsessed with change, and how we change, and what we do to change. But I’m not one of those people who think Werthers are sell-outs because you should be eating toffees out of a paper bag. I’m not one of those ‘in my day all this was fields’ people – but what is happening in London is a gentrification and social cleansing which hasn’t happened on this scale before.

“It is terrifying, it is unsustainable and it is revolting that what we’re seeing is the transformation of London into an investment hub in the sense that where people live they are no longer welcome. The poor must leave. If you don’t earn enough, you must be excluded. You must go, whether it’s through housing benefit caps or through ex-council houses being taken down and redeveloped.”

Thomas isn’t all about the rant. He’s precise with stories and examples and statistics. To back up the argument above, he references Elephant and Castle in central London, where, he says, 3,000 people recently lived on a council estate which has now been transformed into a development with room for 2,500, out of which 79 homes will be socially affordable.

“Socially affordable means 80% of the market rent. No-one who lived there is going to be able to live there now. And then you find out the place is being marketed in Malaysia as an investment opportunity. It is s*** from beginning to end because cities were once the place where people could come to find themselves, to explore who they were, to find new ways of being and existing. They were places to escape to, places where art thrived. And now they’ve become investment opportunities for the mega-rich. I look at this and I look at the Greek debt crisis and I see it in parallel: that the poor are being punished.”

As ever in Mark Thomas’s presence, I feel that I’m learning, I’m laughing, I’m getting angry about things, I’m wanting to do something to make the world right. And that has always been his aim: his shows aren’t a succession of zinging one-liners – although they’ll always make you laugh out loud – because, at the end of the day, he wants his audiences to become activists, even on a small scale. It doesn’t matter if his focus has fallen on weapons manufacturers or the Ilisu Dam in Turkey or the torture trade or the right to protest in Parliament Square or a fizzy drinks manufacturer; buy a ticket for a Mark Thomas show and you’ll leave believing that you’ve regained the right to protest, regardless of the oppressive mood that successive governments and the police have encouraged since those massive marches against the Iraq War.

I ask him about this goal of emboldening his audiences and giving them the courage to stand up against authority. First I get a lesson on the current politician-voter relationship (“It’s the politicians who have become disengaged from us rather than us disengaged from politics, it’s them that have f***ed off”). Then we swerve into problems with the EU (“I love the charter for human rights, I love the fact of freedom of movement – those are really exciting things. I’m not interested in signing up to rolling privatisation and some bankers’ club, which essentially it is”). Oh, and let’s make room for a diatribe against Ukip (“They’re awful racist xenophobic Little Englanders who I’ve always described as ‘the Tory party at closing time’. They’re pathetic nasty f***ing opportunists – the chlamydia of politics”).

Ehm, Mark? Emboldening your audiences and restoring their sense that they have a right to protest?

“People go, ‘But shouldn’t you get permission? You should get permission to demonstrate.’ F*** off. What do you mean, I need permission to demonstrate? If I need to have permission to demonstrate, I can assure you the first thing I will do is have a non-permitted demonstration to demonstrate about the need for permission to demonstrate. The right to protest, the right to free speech, the right to freedom of assembly are all fundamental. We do not have all the rights that we have without the right to protest and the right of freedom of speech. We don’t have them. They don’t exist. These are the building blocks of all our freedoms.”

Thomas’s last two visits to Edinburgh raised the bar, I think. In 2012 he performed Bravo Figaro, which centred on his attempt to get professional singers to perform in his parents’ living room in front of his opera-loving, working-class dad, who had become ill with the degenerative disease Progressive Supranuclear Palsy. It was an emotionally devastating piece that pulled no punches when confronting the difficult relationship between father and son. Then, in 2014, he brought Cuckooed to the festival, peeling back the sordid layers of surveillance and undercover activities. Again, Thomas hit home on an emotional level, detailing his feelings of betrayal when he discovered that one of his best friends and fellow activists from back in the day had been spying for BAE Systems.

In both cases, the personal had begun to affect the audience as much as the politics. The production of each show was also more complex, involving video-screen interviews and perfectly-timed voice recordings and a stage set. This was comedy, yes, but it wasn’t stand-up. It was theatre.

“Basically, what I do is I go off and do things. I make interventions, if you like, then come back and tell the story of it,” he explains. “I’m always slightly obsessed with the idea of how do we tell stories, how do we make sure that they’re true, how do we connect with the truth, how do we document it and how do you get the audience to do things outside of the theatre.

“I can’t see the point of doing something that doesn’t make people feel change in some way. How can you say that theatre and art and comedy don’t change things when the very building block is to change? You go from not laughing to laughing. You go from not crying to crying, not feeling anything to feeling empathy. It’s innately about change. And all I’m saying is, ‘Just make that a little bit bigger’.”

To that end, he may well be in the perfect Edinburgh venue this year: Summerhall, which has quickly gained a reputation as something of a festival within the festival, a fringe within the fringe. Countless interviews currently being published with comedians selling their shows will include fulsome but often woolly praise of how wonderful Edinburgh is at this time of year. Ask Mark Thomas, however, and again he’s unusually precise and knowledgeable.

“I love the fact that you can go to Summerhall and there are exhibitions by Genesis P Orridge and John Berger,” he says. “In a way, what Summerhall has done is reclaim the counterculture. And that’s really interesting: that culturally the programming has done that.”

He starts to rhyme off various things he’s seen there in recent years or who’ll be there this year: Klanghaus and Looking For Paul and Paines Plough and Daniel Kitson and Northern Stage. “You want to be in good company,” he enthuses, “you want to be in company that is like-minded, and so for me the programming there is really exciting.”

Let’s take this opportunity, then, to get an Edinburgh veteran’s overview of the Fringe.

“There are the three venues that stand out for me in Edinburgh during the Festival,” he says. “The Stand, which continually runs really great, value-for-money gigs with a range of comics, empowering local acts to come forward. And of course you’ve got a whole range of really established, really good, class acts that are going to be performing there. Then you’ve got the Traverse, which is an outstanding venue that I adore. I have never seen a festival crew as good as that, shovelling in all these different sets, but also you’ve got an amazing set of writers and directors and performers that are in the building. It’s a genuine thrill to be in there. The other venue is Summerhall.”

He’s also got a word to say about The Arches, having put his name to a petition to keep the Glasgow venue open after its licensed hours were curtailed.

“Look, the thing is, The Arches has produced some really fine and wonderful stuff. Beats, from a couple of years ago, an amazing piece of work by Kieran Hurley. Or Rob Drummond’s Bullet Catch, a beautiful piece. To shut it down just seemed petty and vindictive.

“It also suffers from that fantastically pedestrian and stupid attitude where people say ‘It’s just art’, something that’s an add-on, the Claire’s Accessory of life. It’s not: it’s crucial and it’s fundamental and it’s vital to a whole range of things, from people’s mental health to education to freedom of expression to the economy to being human. You damage it at your own peril.”

In a way, Thomas’s views on The Arches’ closure are linked to the wider theme of his Trespass show, in that it’s about public space, and how that public space is used, and how the people in power will try to limit the public’s use of that public space. For him, though, writing his name on a petition is not usually enough. When he’s in Edinburgh, you can be sure that Trespass will spin off onto the capital’s streets and you’ll see Mark Thomas’s name in a newspaper because of some localised activist stunt he has pulled. And you can be equally sure it won’t be a one-dimensional event.

“I’ve had mates of mine who are artists go, ‘That was great – that’s proper performance art’,” he says of past efforts. “Well, yes it is. But it’s also protest. And it’s also f***ing about. And it’s funny. It’s all those things wrapped up in one.”

Mark Thomas performs Trespass: Work In Progress at Summerhall, Edinburgh at 5pm from August 6-30 (not August 10 or 20)