Stephen Fry is backing a campaign that urges theatregoers to keep their mobile phones turned off during performances as part of a drive to improve audience etiquette. He re-tweeted the link to the online Theatre Charter (theatre-charter.co.uk) after asking followers: "How many times has a mobile gone off when you're at the theatre? Sign and RT."

Richard Gresham, a regular theatregoer from London, drew up the charter after becoming incensed at the thoughtlessness of a tiny percentage of people who ruin performances for audiences and actors alike. It includes a commitment "to never check your phone during the performance for any reason". Since its launch last month he has attracted support from more than 1,250 people.

Gresham, a theatre sales and advertising consultant, sees plays up to four times a week and estimates that 90% of them are blighted in some way by an audience member.

He told the Observer: "I spend a lot of money in the theatre. I was stressed every time in the theatre, thinking, 'someone's going to ruin it tonight'. You either live with stress or have a word with them. Then they have a go at you. I got to the point where I thought, 'I can't handle this any more'."

Mobiles ringing and the glare from smartphone screens lighting faces in the darkness drive actors to distraction. In June the Oscar-winning actor Kevin Spacey reprimanded a theatregoer for letting a phone ring during his courtroom speech in the legal drama Clarence Darrow, saying: "If you don't answer that, I will." In 2012 Jenny Seagrove improvised lines in Noël Coward's Volcano amid incessant ringing: "The world will be a better and more peaceful place in the future. Hopefully, nobody will get around to inventing mobile telephones."

Other courtesies recommended on the charter site include: go to the loo prior to lights down; unwrap sweets prior to lights down or during applause; and never leave mid-performance "unless for medical or emergency reasons. If bored, leave discreetly at the interval."

Gresham is astonished at the noisy unwrapping of sweet wrappers. The other night, in an apparent attempt to do it quietly, someone took a good five minutes to open the "crinkliest packet", he said. "There's no sense of respect," he added. "If we don't do something now, it will become the norm. It is one time in your life when you turn everything off and immerse yourself in the art."

Gresham's recent theatre visits include: to Murder on Air at Richmond, during which three mobile phones went off; to Porgy and Bess at Regent's Park, where someone was busy texting; and to Shakespeare in Love at the Noël Coward theatre, where someone used a phone to film scenes in the first act.

If Gresham taps an offender's shoulder, rows can flare up: "People protest that they must keep in contact with their babysitter or have important work going on. Well, then, don't go to the theatre!" Tweets responding to his charter have not all been supportive: "I've been called 'pompous' and 'middle-class'. But it's just good manners."

If Shakespeare's groundlings had had mobiles, they would no doubt have used them, just as they customarily ate and talked through performances. "It would be mayhem," Gresham agreed. "But that was theatre etiquette in those days. Mobiles have changed things about the way we interact."

Terri Paddock, a theatre commentator who is spreading the word about the charter on Twitter, said: "It's staggering how often it happens. It makes the [actors'] job much more difficult, because they feed off the energy of the audience."