They were joined by a group of female proprietors, directors and performers at the currently shuttered Lyric Theatre on Shaftesbury Avenue at noon on Thursday.
Their “silent stand” called for theatres to be allowed to reopen without social distancing and highlighted a perceived lack of Government guidance on the issue.
Theatre director Caroline Jay Ranger, theatre owner Nica Burns, musical theatre star Melanie Marshall and actor Anna-Jane Casey were among those taking part.
Wolverhampton soul star Knight said: “I performed at the UK’s first indoor socially distanced show at the London Palladium with Sir Andrew Lloyd Webber.
“I know first-hand what it took to make that show happen, to make it Covid safe both front and back of house.
“I also know that with the current social distancing rules in place, venues cannot reopen.
“That means hundreds of thousands losing their jobs in specialist areas of employment, adding to the number of people who will lose their jobs once furlough ends. People need hope. Please, give them some.”
French said: “Today’s silent stand with my fellow female colleagues from the theatre world is so important. We need the Government to listen and take action before it is too late.
“Already we have seen several theatres around the country close, which is a huge tragedy. Today’s stand is on behalf of everyone in the industry who has had their livelihood affected.
“We need a date from the Government to get theatres back open – safely of course – but as soon as possible, so the terrible erosion of UK theatre does not continue.”
Last week, Nimax Theatres announced it will reopen all six of its West End venues – including the Lyric – from October for a season of socially distanced shows.
However, reduced audience numbers mean they will run at a loss.
Nimax co-owner Ms Burns said: “As Culture Secretary Oliver Dowden said, ‘Theatre is a lynchpin of London’s West End and its absence is painfully reflected in its deserted streets’.
“Today we stand for the army of talented theatre-makers and support teams ready to work, entertain and help reinvigorate the economy.
“We will do everything we can to assist the Government to reopen our theatres safely without social distancing.
“We look forward to the day when every theatre in the UK is ablaze with lights.”
Marshall was playing Mrs Obooko in Only Fools And Horses The Musical before the Theatre Royal Haymarket closed in March.
She told the PA news agency the news they had to close was “a massive shock”.
She added: “We had just put a new cast in and they had done about five weeks of the new cast.
“We were still rehearsing at that time and putting new understudies in and suddenly everybody was out of the building.
“We sensed it would go on longer – it is a pandemic and a virus, so we all had the sense this wouldn’t be a three-week thing and it would go on for months.
“Everybody got their heads around possibly having to wait until September, October, November.
“We were a little bit cautious and decided on November and especially when we knew furlough was dropping off at the end of next month.
“It was a seamless way of trying to get hundreds of thousands of people back to work, trying to open in November.
“But the way the Government are behaving, this is not going to be possible at the moment.”
The Lyric will reopen with Six – the first musical to resume performances in a West End theatre.
The show is a modern retelling of the lives of Henry VIII’s six wives, presented as a pop concert, as the women tell their own stories.
It will temporarily move from the Arts Theatre for an 11-week run with social distancing from November 14.
The gathering came as Westminster City Council announced the Inside Out festival involving theatres, opera houses, museums and galleries.
It said it wants to attract visitors back to the West End with performances, exhibitions and installations, in the four-day event from October 1.
Events include open-air performances from West End musicals, the Royal Opera House, English National Opera, and the Royal Philharmonic Brass Ensemble, an open-air gallery on the National Gallery’s North Terrace, on Trafalgar Square, and light projections on to Marble Arch.
Council leader Rachael Robathan said: “We’re delighted to be working with our cultural partners to give people a chance to sample the magic of stunning theatre, music and art on our beautiful streets and squares. We hope this is the precursor to a full reopening of the West End when we are sure it is safe to do so.”