The producer of the cult film "Monty Python and the Holy Grail" took its comedy stars to court on Friday in a bid for royalties from a hit spin-off musical, Spamalot.

Three of the six Pythons -- Eric Idle and Michael Palin, both 69, and Terry Jones, 70 -- are due to give evidence in the five-day legal action brought by producer Mark Forstater at the High Court in London.

Spamalot, created by Idle and described on posters as being "lovingly ripped off" from the 1975 Holy Grail movie, has played in London and on Broadway and any royalties would likely run into hundreds of thousands of pounds (dollars).

Tom Weisselberg, the lawyer representing Forstater, told the court that his client was in "difficult financial circumstances and has been forced to bring these proceedings".

Weisselberg said both sides agreed that the film producer was entitled to a share in merchandising and spin-off income from the Holy Grail, but a dispute arose in 2005 as to the extent of his entitlement.

The lawyer said people involved in drawing up a 1974 agreement about royalties from the film "understood that, for financial purposes, Mr Forstater was to be treated as the seventh Python."

Forstater should therefore be entitled to a seventh of merchandise revenues allocated to the Pythons' company, Python (Monty) Pictures Ltd (PMP), Weisselberg argued.

But the producer was told he was only entitled to one-fourteenth and has been paid on that basis since 2005, the court heard.

John Cleese and Terry Gilliam are abroad and are not expected to give evidence in the case. The sixth Python, Graham Chapman, died in 1989.