Cinemagoers attending a screening at one of the most successful – and left-leaning – arthouse venues in Britain on Sunday night had to pass a picket line of staff demanding the London Living Wage.

Ticket sellers and ushers at the Brixton Ritzy in south London have been striking every Sunday for three months, but last night the protests intensified as management for the first time staged a screening during a walkout.

As a result, anyone hoping to see a live streaming of Monty Python’s live show from the O2 Arena was confronted by a protest swiftly nicknamed “Monty Python’s Flying Picket”.

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The Ritzy – normally a middle-class haven where customers enjoy documentaries and arthouse films – was last night hidden behind metal screens erected, in the words of a grim-faced manager, “to make for a more comfortable experience for our customers”.

Anyone wishing to enter had to go through a narrow opening in the screens and pass a picket line of staff waving banners and chanting slogans.

The Monty Python screening was advertised with the tagline “Always look on the bright side of life” – but the strikers surrounding the cinema had just hours earlier received the backing of one of the Pythons themselves.

Urging his fans to stay away from the Ritzy screening, Terry Jones tweeted: “Python fans. Ask for your money back for Ritzy Cinema Brixton. The management are refusing to pay the staff Minimum London Wage.”

Jones added his voice to 7,000 people who have already signed a petition supporting the strikers in their demand for the London Living Wage of £8.80 an hour. Signatories include the comedian Russell Brand, footballer turned actor Eric Cantona, and film makers Ken Loach and Mike Leigh.

It was a far cry from the Eighties, when the Brixton Ritzy was considered so synonymous with left-leaning causes that the then manager had to place an advert in a local newspaper telling potential customers that not every film shown was “left-wing or gay”.

As strikers chanted slogans on the other side of the metal screens, Lyn Goleby, the managing director of Picturehouse Cinemas, which owns the Ritzy, insisted her staff were getting a good deal on £7.53 an hour plus £1 if customer service targets are met.

She said: “We are one of the highest-paying cinema operators in London. Only about 250-odd companies signed up for the London Living Wage, and you won’t find many cinemas and retailers among them. It’s not viable for these kinds of businesses.” She claimed only four people had phoned to cancel their tickets, “and only one specifically said it was in support of the strike”.

But Rob Lugg, a Ritzy usher and Bectu union representative, who organised the strike, pointed out that Picturehouse’s latest accounts report “an excellent year” with a “significant increase” in operating profits to £1.3m.

One customer ignoring the strikers was Jessica, who said: “I feel uncomfortable about crossing a picket line and I have sympathy with their cause, but this was not any old film. It’s a live event and it’s a special birthday treat for my 11-year-old son, who is a massive Python fan.”