Terry Gilliam: still animated, but not walking quite as silly a path as he once was

He is the Monty Python animator-turned-film director famed for his manic creativity, who reinvented himself again earlier this year with his operatic debut, Berlioz's The Damnation of Faust.

But now Terry Gilliam, 70, is slowing down. Not only does he reveal that he is struggling with his second operatic work at English National Opera, he also thinks his film career is over.

"I've actually reached the point of not believing I'll ever make a film again," he says. "I am reminded by my wife that I always feel like that. But the great thing about getting older is that your memory goes." Gilliam and the Python gang, however, remain inescapable 42 years after they first silly-walked onto British television.

Later this month a BBC comedy-drama, Holy Flying Circus, will explore the controversy surrounding the Pythons' 1979 religious satire The Life of Brian. It focuses on incidents including a notorious 1979 television debate between John Cleese, Michael Palin, the Bishop of Southwark and noted Christian Malcolm Muggeridge.

At the moment, a play at London's Hampstead Theatre, No Naughty Bits, examines the group's 1975 legal battle against censorship by US television network ABC and Gilliam is interviewed in Martin Scorsese's documentary about Beatle George Harrison, which is out on DVD today.

Faust, which garnered some of the best reviews of Gilliam's career, will be broadcast for the first time on television on BBC Four on Friday. A busy tume, but Gilliam still has creative doubts. He says his next opera will also be by Berlioz – Benvenuto Cellini, a 19th-century two-act opera loosely based on the memoirs of a Florentine sculptor, which is so technically difficult it is rarely performed.

"There is a discussion going on," he says. "The problem with me is that opera is so far in advance, it would be a year and a bit away. And I can't do that, that's what I've told [ENO artistic director] John Berry. He wants to do something in 2013, but I can't definitely say yes until I know whether I'm shooting a film next year."

He says the prospect of directing another opera is "frightening". "I've got all excited about a particular opera, I love the music, but I've been stuck," he says. "I haven't had the epiphany which I had with Faust."

Gilliam has a history of diving into the unknown. Born in Minnesota in 1940, in previous interviews he has described moving to England after becoming disenfranchised from the 1960s US political landscape.

Meeting three future Pythons through children's TV series Do Not Adjust Your Set, he became the group's animator whose visuals were a key element in the show's success. Post-Python he reinvented himself as a film director, taking on unconventional projects like 1981's Time Bandits. The movie was produced by HandMade Films, which George Harrison co-founded.

Gilliam's conversational style is scattergun; one minute he seems bored, the next more focused. He is modest about his achievements with Faust, in which he transferred the legend to Germany in the 1930s.

He says he still has reservations about opera as an art form.

"When it works, opera is extraordinary. It's like bullfighting. But most of them are just crap. Extraordinary sets, amazing singing, but crap. People are spending 90-odd quid to sit in those seats and they're getting a rotten deal. My approach was always: 'we are doing a show here'."

With Benvenuto Cellini, he says: "It doesn't get done very often, so it will stand on its own two feet. I don't have a clear idea and that's why I'm worried. I have detail, but how do you do it? It's stunning, even better than Faust.

"The plot is silly; a comic opera. But it doesn't leave me all the room I need to shape it. The characters say what they say and do what they do."

Gilliam sounds frustrated by being torn between directing operas for small, appreciative audiences and winning financing for his filmmaking first love. Movie projects in development include an adaptation of Paul Auster's 1994 novel, Mr Vertigo.

His short film, The Wholly Family, is touring the festival circuit.

"I just know I need to get shooting because it's been three years," he says. "Nothing is back on track. Film is difficult to get funding for unless you're doing a huge movie in 3D."

Gilliam's troubled, longstanding attempt to adapt Don Quixote "just needs one more person to come in," he says with a wry smile. "I just want to concentrate on those films," he adds. "I get easily distracted and greedy to do lots of films. I used to believe I could will things into existence, but now I am older I know it doesn't work that way."

So what does he think about the current revival of interest in Python?

"I've had no involvement," he says of Holy Flying Circus. "I just met people yesterday who've seen it and they said it's really funny. The thought of Python stopping anyone... One of our members was making phone calls. Just stop it. Just stop it."

Holy Flying Circus, written by Tony Roche, co-writer of The Thick of It, is billed as a "fantastical reimagining" but John Cleese and Iain Johnstone, who produced the original TV debate, have protested against the forthcoming show's historical inaccuracy.

A source close to Cleese said he offered to meet the producers, Talkback Thames and Hillbilly Television, but the meeting never occurred. The source said Cleese had subsequently seen a copy of the drama's script and was "disappointed by its content".

Gilliam, meanwhile, still defines himself as a Python, 40 years on. And he remains a risk-taker. "Jumping off cliffs is much more interesting than jumping off a table," he says.