Scottish artist Peter Howson's torment laid bare

• Driven to the brink: Peter Howson

Even by the standards of Peter Howson's turbulent life story - from war artist to battles with drug addiction - the story of his painting of St John Ogilvie became a disaster-stricken saga, a new documentary reveals.

In 2008 Archbishop Mario Conti commissioned Howson to produce a depiction of the scene of the Scottish saint's martyrdom to mark the planned renovation of St Andrew's, the mother church of Scottish Catholicism. It was to be unveiled for the visit of Pope Benedict XVI, planned as a vast crowd scene, about eight by six metres in size.

But in the next two years Howson reached a new low in his struggle with mental illness, diagnosed with a severe form of autism even as he was made an OBE by the Queen. He placed his business affairs in the hands of legal guardians after it emerged a former manager was a convicted drug dealer.

"I understood what it was like to be in the mind of a madman," Howson says in the film. "It's not a very nice place to be. You don't know what I'm like. You don't know how mad I am."

The Madness of Peter Howson is broadcast on BBC2 Scotland on Monday night. It is narrated by actor Peter Capaldi, who describes the painter as a man "with a turbulent past and a present haunted by financial problems".

The Glasgow archdiocese provided Howson with a disused church in which to paint what it called "the most important commission for a Scottish Catholic Cathedral since the Reformation".

• Peter Howson: Deep scars of war experience

Assistants knocked giant letter-box shaped holes in the brick walls to take a series of large canvases into the building. But as the renovation of St Andrew's was delayed in a contractor row - it will now reopen next year - Howson took nine months to start and sold his collection of books to pay for paints. He finally abandoned the project for a smaller, single canvas, which he then painted over after weeks of work.

The image of St John Ogilvie, who was hanged and disembowelled in 1615 after being convicted of treason for leading a Catholic mass, was unveiled in a muted ceremony earlier this year. The final, single image of the saint was a fraction of its planned size.

"It was going to be a lot bigger, and it was going to be one of the largest crowd scenes in art history, but I worked on a painting for about nine months and then in one moment I completely destroyed it. A bit like Blue Peter, I had one prepared earlier," Howson said."It's a dark period. I fought my way through this, but I'm still not completely out of the woods," he added. "It's about time I got on to a new chapter, because this chapter is starting to get really boring now."

A new series of Howson's paintings of Robert Burns are to be unveiled for the opening of the new Robert Burns Birthplace Museum in Alloway next month.

In the film Howson's long-time London dealer Matthew Flowers confirms that both David Bowie and Madonna collect the artist's work.

Actor Steven Berkoff, an Edinburgh Fringe favourite, shows his own collection in the film. He said: "Having Howson in my life has in some way given me a sense of what I am.

"We need artists like we need lightning rods … It is the artist who is struck and scarred and burned by the lightning."