The story of the Tolpuddle Martyrs, the six Dorset farm labourers who formed the first trade union to protest at wage cuts, took place at a time in the first half of the 19th century when ballads and folk songs were being written and sung about all sorts of social and political upheaval.

And yet, no songs appear to have been created to chronicle this major event in English history, or at least none survive, as far as John Kirkpatrick has been able to discover.

This lack of material might be seen as a drawback for Kirkpatrick, the hugely experienced singer and squeezebox player whose musical associations include singer-guitarist Richard Thompson and folk bands Steeleye Span and Brass Monkey, in contributing relevant music to a play depicting the Tolpuddle Martyrs' leader, George Loveless, and his and his wife, Betsy's fate.

"On the other hand," says Kirkpatrick with some glee, "it gives you a completely free rein to write what you like."

Kirkpatrick's involvement in combining theatre and folk music goes back to the 1970s with twin productions that meant less then than they might do now - Lark Rise and Candleford - and although he's been more concerned in playing and teaching music in recent years, his experience in theatre has proved valuable in creating We Will Be Free, at the Assembly Rooms until August 25.

"You get to see how songs and music can help to move the drama along," he says. "Often the music that accompanies a play will say more than a long speech or scene. It can create a change of mood in a short, snappy way and it's basically a great vehicle for carrying the narrative."

Folk musician Kirkpatrick was familiar with the Tolpuddle Martyrs story and aware of the voices of the working people, making themselves heard, at a time when topical broadsides were being published and the ballads and songs that make up a big part of what we now call folk music were on people's lips in the same way that pop songs came to be later.

"It was odd in a way that we couldn't find anything directly relating to the story because the martyrs were transported by way of punishment and that's quite a common theme in folk songs," he says. "But this was a time when almost everyone believed in God and went to church or chapel every Sunday and the main character, George Loveless, was a Methodist preacher, as was one of the other workers involved. So we looked at hymns and I found a Chartist hymn book from around the same time, and we were able to use two or three of these to bring some authenticity and there are a few traditional songs that fitted the emotional context at various stages of the story."

Kirkpatrick also drew on his own song-writing skills and he's happy to concede that working alongside Richard Thompson (he played on Thompson's classic Hand of Kindness album and toured with Thompson's band for many years) has benefited him as a songwriter.

"Richard has written an amazing range of songs, some of which are in a traditional folk style and others are quite far removed from folk music," he says. "But you can't help but learn from a master like that and there's a certain turn of phrase he'll use that, if you can adapt it and include it, is a gift.

"One of the new songs in the play is called Beneath the Sycamore Tree, the tree being the main focal point in the village and the scene where quite a lot of the events in the story took place.

"I suppose everything I've done musically has fed into that song in some way."

Although he arranged and rehearsed all the music, Kirkpatrick doesn't appear in the play as Gore and Elizabeth Eves, as well as playing several characters, sing and play a handful of instruments between them: button accordion, piano accordion, fiddle, mandolin and mandola.

"They sing solo and together, accompanied and unaccompanied and one can be playing tunes while the other's offstage changing or they'll be playing together," he says.

"So you get quite a full range of folk music and considering the basic material that Neil developed the script from was pretty dry - the newspaper reports of the time sound very dry to our ears and the letters he drew on were very formal - it's turned into a very human telling of a powerful story."

We Will Be Free! is at the Assembly Rooms, George Street to August 25 at 12.30pm