How do we begin to heal divisions that seem almost insurmountable? In a world of increasingly polarised politics and an ever-widening gap between rich and poor, it's a question that's on almost everybody's minds. There may not be any easy answers, but in his new play, The Seven Acts of Mercy, opening at the RSC's Swan Theatre this November, Anders Lustgarten reminds us that compassion and understanding must be at the heart of any solution.

After waking up to the news of what's been widely viewed as one of the most significant political events of a lifetime – the US presidential election victory of Donald Trump – we met up with the playwright and activist to discuss his story, its artistic inspiration and the importance of nurturing hope and optimism even in the most troubled times.

“There have been a lot of hugs this morning,” he owns, shortly after leaving the rehearsal room. “But it's good to be doing something positive and collaborative by working on a play – particularly this play. It is about compassion and the extreme difficulty of connecting and trusting other people. You won't find a play that is as up-to-date about 2016.”

There are two timelines in this story, one taking place in present-day Bootle, the other in 17th-century Naples. The former begins with ageing docker Leon (Tom Georgeson) delivering an impromptu art history lesson to his fidgety grandson Mickey (TJ Jones), with particular emphasis on a favourite painting – Michelangelo Merisi da Caravaggio's masterpiece, The Seven Acts of Mercy. The title comes from the Catholic Church's idea of “Corporeal works of mercy”, essentially a set of charitable acts that minister to bodily, as opposed to spiritual, needs. These are, in Leon's words: “Giving food and drink to them as needs, taking in a stranger, clothing the naked, supporting the sick, visiting the incarcerated and burying the dead.” In an attempt to cheer up his grandad – who is not only ill but facing the threat of imminent eviction – Mickey sets out to perform his own version of the seven acts, visiting a food bank and getting embroiled with violent gangsters in the process. Meanwhile, their world is further shaken up by the reappearance of Mickey's dad, Lee (Gyuri Sarossy), a failing businessman who turns out to have his fingers in some very unsavoury pies.

“It's looking at the implications of the sort of social changes that capitalism is undertaking in places traditionally occupied by workers, in terms of the crushing of the welfare state and the gentrification of poor areas,” Lustgarten explains. “So many people have been laid off, and it's made them... ill, really. There's been a fundamental transformation of the function of the working class in this country, from being workers for about 200 years, to being turned into consumers, to no longer being needed by financial capitalism at all, which is why the political elite thinks it's okay to just let them decay. There are was an interesting article in the Guardian the other day about how at least half of all benefits claims come from formerly industrial areas deliberately smashed by Thatcherism. When you take people's work away, you take away their sense of who they are and you make them isolated and fearful and ill.”

Flashback to 1606, when the brash, bullish and brilliantly foul-mouthed artist is beginning work on the commission that would go on to inspire this very play. Having made himself some powerful enemies back in Rome over the small matter of murdering one of their men, Caravaggio (Patrick O'Kane) is at this point hiding out in Naples – though is being less than diligent about keeping a low profile. The connection between the past and present world lies in his choice of subjects – typically for Caravaggio, the painting is populated by the kinds of thieves, beggars, prostitutes, gangsters, fellow artists and ordinary people who inhabited his life. In the play, one of the central characters is a prostitute called Lavinia (Allison McKenzie) who models for the painting – an astute and witty foil to Caravaggio who turns out to have her own passion and critical eye for art.

“I saw the painting in Naples a few years ago, and there's just something about the immediacy and visceral intensity of his work that catches you. The people in his paintings are very recognisable as real people, poor people – people that he knew. In the context of the kind of art the rich and powerful tended to produce, there's something quite radical about that. There's a kind of intimacy and understanding, and they're also very dramatic, theatrical works, with chiaroscuro and a kind of luminous quality.”

In many ways, it's hard to resist drawing parallels between the fictionalised artist within the play, and those of the playwright himself, both aiming to give voice to the poor and the marginalised in spaces not usually reserved for them.

“Caravaggio recaptures the space which is controlled by the financial and political elite for normal people, for his people, by representing them in that space. Because of the way in which working class people are depicted in the media in fiction now, it's almost become radical again to show them as they really are. You see how much of an impact something like I, Daniel Blake is having just because it shows working class people as fundamentally real people, with art and dignity and troubles. Whereas the sort of Benefits Street type caricatures are what serves the ruling class, because if you present people as greedy and meaningless, then it's okay to starve them on benefits and ignore them in the House of Commons."

Of course, unlike Lustgarten, Caravaggio was working with the knowledge that “his people” would see the work that he was doing, since at that time, everyone from every walk of life was more or less obliged to go to church. Theatre audiences, on the other hand, are self-selecting, and it's hard not to acknowledge that the social milieu from which they're drawn has steadily narrowed over the years. How, then, can Lustgarten be sure of reaching the people he's writing about?

“There are two answers to that, one of which is that the middle classes are absolutely the people that need to be reached,” he replies. “When I went to see I, Daniel Blake, I was astounded by the number of people sitting in the room who clearly had no idea about the stuff that's going on around them. And there's a part of me that thinks, 'Why don't you know this? You really should know this!' But it's always surprising to people who are politically active how much other people don't necessarily know, as we've seen in the election yesterday. We do fully intend to take the show to Liverpool afterwards, but it's almost precisely because this is the archetype of comfortable Middle England that it's the perfect place to do it.”

“I do also find that my plays tend to attract the people they're written about, though. I wrote a play about the BNP called A Day At The Racists, which was set amongst a group of painters and decorators in Barking, and we had a whole heap of painters and decorators from Barking come all the way to Finborough in West London because they'd heard about this play. These are not people that would ever go to the theatre, so how they heard about it, I don't know, but they did and they came. I also wrote a play called Lampedusa last year about migration, which referenced the drowning of Eritraean people. We had a huge contingency of Eritraean people turn up and thank us for telling their story in a way that didn't stereotype them or make them look like parasites.”

If the tour goes ahead, it will be interesting to see how responses in Liverpool compare to those in Stratford – while some of the events we see unfolding in the play are equally relevant elsewhere in the country, the choice of setting was an important one for Lustgarten.

“Liverpool's a brilliant city! It's a bouncy, energetic, mental, combative, impassioned, sentimental, marvellous city. It's also very like Naples was then in terms of being a feisty, tribal, largely working class, very insular, very proud kind of city. Liverpool has probably seen some of the most rapid changes in terms of the balance of power in recent years. When the docks were strong, a strike could bring the whole country to a halt, but all that power is now gone. It's an interesting measure of the trajectory of British socialism - it's very difficult to have socialism if ordinary people don't have a way of stopping the system that governs them.”

Of course, part of the reason for the change in theatre audiences has been the advent of other, more readily accessible media, from radio and cinema to television and the internet. Nowadays, it's difficult for anything to compete with instant entertainment at the touch of a button. Nevertheless, Lustgarten, who has dabbled somewhat half-heartedly in screenwriting, still believes that theatre possesses a unique power.

“TV's a weird world because there are so many people making artistic decisions, so in a way it ultimately comes down to how much you're willing to compromise and sacrifice the things you want to say and how you want to say them in order to obtain a wider audience. And I think the answer is, not very, in my case!” he laughs. “I do also think though, that you shouldn't confuse lots of people watching it with it being more important or meaningful. There's something about theatre as a medium that is much more intense. It naturally establishes an emotional connection, because you're there in the room with people, watching them go through things and struggle to achieve things.”

He'd know, of course – this is a man who got into playwriting while teaching in a prison and witnessing the impact of performance on the inmates. As passionate as he obviously is about art, he's said before that his writing will always be secondary to his activism – though that implies a more clear-cut distinction than is perhaps fair. For him, both are clearly born of the same desire to highlight the injustices of the world and both play a part in the search for better ways of living. Even on a micro level, Lee's and Mickey's struggle to reconcile could stand-in for the pressing problems faced by all of us today.

“The cheesy version of this play would be one in which Mickey does all the Seven Acts and they're all really good and successful and Leon would be like, thank you, now I can die in peace. But it doesn't work that way. I think the intense sense of emotional confiding and openness in this play is extremely optimistic in a world in which we're all really afraid, never more so than this morning. The ability of people to trust and connect to one another and to love one another in a world in which we're fucking terrified of what the scum in charge are gonna do to us, is more than optimistic. It's absolutely essential.”

The Seven Acts of Mercy is at the RSC's Swan Theatre from Thursday 24 November 2016 until Friday 10 February 2017.