Michael Palin, Eric Idle and Terry Jones arrived together and sat at the back of a small, modern courtroom to listen to opening arguments in the case. All three are expected to give evidence next week.

The Pythons are at odds with Mark Forstater, the producer of the "Holy Grail", who says he has not received his fair share of profits from "Spamalot", a spin-off musical.

Inspired by the original film, the musical opened on Broadway in 2005 and has enjoyed a successful run in Britain too. Idle wrote the lyrics and collaborated on most of the music.

Forstater, an American based in Britain, says that under a 1974 agreement between him and the Pythons, he is entitled to one-seventh of profits derived from "Holy Grail" and any merchandise or spin-offs (MSO).

His lawyer, Tom Weisselberg, told the court that for the purposes of profit-sharing, it had been agreed in 1974 that Forstater was "the seventh Python".

"Spamalot is a spin-off from the film and has been a huge international commercial success," Weisselberg said in his opening argument.

He said that Forstater had been receiving his seventh of the profits from "Holy Grail" until 2005, when the Pythons had unilaterally reduced his share to one-fourteenth.

In court, Forstater sat with his lawyer, with the Pythons behind him. They did not talk. The Pythons listened with serious faces and exchanged occasional whispers.

Forstater told Reuters outside the courtroom he had tried to resolve the dispute with the five surviving Pythons: Idle, Palin, Jones, John Cleese and Terry Gilliam, but that talks had failed.

He said the amount he believed he was owed in relation to Spamalot was 250,000 pounds ($400,000).

The three Pythons present in court declined to comment on the case. Palin told Reuters he was there to observe and would "do my bit in court when the time comes".

The trial is scheduled to last four to five days.

(Reporting by Estelle Shirbon, editing by Paul Casciato)

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