Nine years ago a group of Cornish fishermen were singing sea shanties in their village pub when a holidaying music executive came in for a pint. The result was a million-pound record deal and chart-topping success. But the fishermen did not give up the day jobs. Now they are working the boats, singing and coaching actors for a major British comedy based on their remarkable story.

Filming has just begun for Fisherman’s Friends in the Cornish village of Port Isaac – and so far a good time is being had by all.

Writer-producer Meg Leonard said: “A film community is embracing this fishing community and making them feel a part of it. We’re off now to the pub to meet the fishermen and the cast, and they’ll all have a sing-song together tonight.”

The fishermen are working the boats for the film-makers and guiding the actors on Cornish accents and dialects, as well as coaching their singing.

The singers – aged from 36 to 68 – include fishermen Jeremy Brown and Jason Nicholas, and former lifeboatman Jon Cleave. They have inspired fictionalised characters played by a British cast that includes Daniel Mays, James Purefoy, David Hayman and Tuppence Middleton.

Brown and his son Tom, a sixth-generation fisherman, have been skippering a family boat for the film-makers. Nicholas has been showing them the ropes – literally – warning of the risks in hauling up lobster pots: “In every corner of a boat there is a danger. The pots are in long lines of 40 or 50, all attached to a rope. The weight is horrendous. You’re not going to stand a chance if you’re tangled up in that rope. You’ve always got the risk of being dragged over the side.”

Nicholas is happy that the script conveys the hardship of a fisherman’s life. He is usually on the water by 4am, depending on the time of year and the weather, often working until 9pm.

Singing, he says, is an integral part of his and his colleagues’ lives: “A lot of singing goes on in the pubs here. All of a sudden, someone will start. Before you know it, everybody’s joined in.” Asked about the fishermen’s success, manager Ian Brown said: “It’s a combination of things. When you see them, you want to be in their gang.” The film will tap into British comedies such as The Full Monty. Co-writer Nick Moorcroft says it “celebrates the power of community”.

Cleave now runs a gift shop. Asked what he hopes the film will do for audiences, he said: “I hope they’ll come away with a really warm feeling [and that it] encourages lots of people to go out and sing.”