FOR someone with such a remarkably colourful, cosmopolitan and successful background he wears anonymity well. It’s a wet Wednesday lunchtime in an Italian restaurant off Leith Walk and the country’s most successful scriptwriter goes unrecognised by all, except for the owner, and then only because Paul Laverty lives nearby and is something of a regular.

The screen-writer is casually-dressed, easy company, passionate, as you might expect, when it comes to politics. His latest film, with long-time collaborator director Ken Loach, has won a Palme d’Or at Cannes and is performing excellently at the box office. I, Daniel Blake - inspiring and anger-making, rather than dispiriting - is about a man who suffers a heart attack and is chewed up and spat out by the welfare system, and a young woman, mother of two, who is also a victim of Tory austerity and welfare cuts.

Laverty, who supports Scottish independence, has used the themes of film to highlight a series of important social concerns - many though the pages of the Sunday Herald. He's called for free tampons, for Holyrood to act as a shield against Tory austerity, he said an independence Scotland would benefit the poorest in society - and today he is throwing his weight behind a citizen's income.

If there is a constant to his screenwriting, and there is, it is a robust sense of injustice, whether at home, as in the latest film, or in Los Angeles with Latina workers in California struggling to unionise, or in Nicaragua, in his first film with Loach, Carla’s Song. But his work is in no way didactic, shot through as it is with shards of comedy and, occasionally, romance.

It was Nicaragua which forged the partnership with Loach. In the late 1980s Laverty contacted the director with the idea for Carla’s Song, in which Robert Carlyle, as a Scottish bus driver, takes a Nicaraguan refugee back to her homeland. It’s a country he knows well. During the mid-80s he went there to work as a lawyer for a domestic human rights organisation which provided hard evidence of human rights abuses during the war between the elected Nicaraguan Government of the Sandinistas and the US-backed Contras. He lived in the country for almost three years.

Laverty has had something of a nomadic life. He was born in Calcutta, India, to an Irish mother and Scottish father, he obtained a philosophy degree at the Gregorian University of Rome, and then a law degree at Strathclyde University.

He practised as a lawyer briefly working alongside Kenny MacAskill, then a young radical lawyer, who would go on to serve as the justice secretary in the first seven years of SNP Government. And is also a regular here at the Jolly Ristorante, as are several other well-kent SNP faces like Alex Salmond.

His first collaboration with Loach, however, was not behind the camera, but in front of it, a cameo in the Spanish Civil War drama Land and Freedom, starring the Spanish actress who became his partner, Iciar Bollain. The couple have three children and are settled in Edinburgh.

But it’s not the past Laverty wants to talk about, it’s the future. He is backing a citizen’s income, a guaranteed sum for every adult, which would protect the lives of those affected by swingeing welfare cuts and make it less likely that they are forced to rely on food banks, like the people he met up and down the country researching I, Daniel Blake and portrayed in it by characters such as a single mother of two Katie, played by actor Hayley Squires, relying on free food due to the lack of state support.

Laverty said a citizen’s income would offer much needed protection to the Katies of the real world, and the Blakes - the character in the film loses his entitlement to disability allowance and is left without any income.

Laverty insists this is something which would "release great human energy" instead of people being placed on "punitive" Department for Work and Pensions (DWP) schemes.

It is a proposal backed by the Scottish Greens and is being considered by shadow UK chancellor John McDonnell.

"It should be discussed and a national debate should be started about the proposals,” Laverty maintains. “I, Daniel Blake showed how the cruel the existing system is in terms of how many vulnerable people are sanctioned...The Daniel Blakes of this world would be liberated and there would be potential to release great human energy instead of pushing rocks up the hill like Sisyphus which is punitive and is making people ill."

Laverty said a growing gap between the rich and the poor made the case for a citizens income more pressing to tackle widespread inequality and argued that it had to be part of a response by the left to the to the rise of Donald Trump and Nigel Farage. All the more needed, he continued, due to automation and the jobs losses caused by work traditionally carried out by humans being taken over by robotic machinery.

“More and more jobs are being automated and a huge number have been destroyed by austerity. A polarisation of wealth and increase in the gap between the rich and poor also demonstrates the case for radical action and a great sense of urgency.

“There are no easy answers, but it would put an end to the vicious and dysfunctional welfare system we have. It’s time for great creativity to imagine another way. We have to build after Trump and put forward an alternative to Trumpism and Farageism.”

Creative imagination would feature prominently on Laverty's CV - if he had need for one any more.