Spamalot is based on the 1975 film "Monty Python and the Search for the Holy Grail," which Forstater produced. The musical featured a book and lyrics by Eric Idle, one of the original Pythons, and music by Idle and John Du Prez. Spamalot was described as having been "lovingly ripped off" of the film.
Forstater's lawyers claimed it was agreed that he would be "treated as the seventh Python" financially and would be entitled to the same share of "Holy Grail" merchandising and spin-off income as the other members.
That amounts to one-seventh of the first 50 percent of income from Spamalot, but lawyers for the Python troupe said he was entitled only to one-fourteenth.
Python member Michael Palin denied Forstater's claim to have helped written the film.
"There were six of us. We were a tight group. We wrote our own material," he said in a statement.
Judge Alastair Norris ruled in favor of Forstater in his suit against the five surviving Pythons: Palin, Idle, Terry Jones, John Cleese and Terry Gilliam. The sixth member of the troupe, Graham Chapman, died in 1989.