Simon Callow is trying to say no, once more, with feeling.

“I’m not very good at the word, you see,” he says, rolling his vowels in an exaggerated fashion. “No, no, no. No, you see? I simply can’t do it.”

The 59-year-old actor, still best known for playing Gareth in Four Weddings and a Funeral, is a self-confessed workaholic. Ask him what he’s been up to lately and he reels off a list of projects longer than Hamlet.

This year alone he has toured with Thea Sharrock’s acclaimed production of Equus by Peter Shaffer, performed Shakespeare's sonnets at the Stratford Festival in Canada and is midway through the third and final volume of his epic biography of Orson Welles (although like most writers tumbling towards deadline, he doesn’t like to talk about it).

“I like to work,” he explains. “I’m always slightly afraid not to be terribly busy.”

A fortnight in Edinburgh is blissful restitution for Callow. He returns to Charles Dickens, whose work he could recite standing on his head, covered in silver paint in Princes Street, if he were so inclined. He will in fact perform in the Music Hall of the Assembly Rooms, where he will read two Dickens stories: Dr Marigold and Mr Chops, the Dwarf.

He also appears at the Festival of Politics, in a discussion called Gladder to Be Gay? Callow will share his thoughts on changing attitudes to homosexuality over the past 40 years. As one of the first well-known British actors to come out — in his 1984 book Being an Actor — he is well placed to assess whether the UK is now a better place to be gay.

“There’s no possible comparison with the way things are now from the way they were in the 1960s. It is an absolutely transformed situation,” he says.

“There are things that have been lost and things that have been gained. I think many people miss the gay subculture. A lot of people found it exciting to do something that was against the law, they loved having codes. The problem was everybody had to have those codes whether they wanted them or not.”

One person who won’t be practising his secret signs is Joseph Devine, the Roman Catholic Bishop of Motherwell, who in March criticised the gay community’s attendance at the annual Holocaust memorial service and the decision to make Sir Ian McKellen a Companion of Honour for “services to drama and equality”.

“The bishop is in my view a profoundly ignorant and stupid man,” says Callow. “If he finds it offensive that gay people want to celebrate those gay people who died in the Holocaust — which was a large number of people — he’s also profoundly un-Christian.

“But then all churches have thrived on prejudice, it’s a means of keeping people under their control. I think they are really, really shocked at how quickly the world has moved on. They are constantly evoking some kind of specious moral authority which they’ve taken on. Nobody has particularly asked their advice on matters moral. We are working them out for ourselves.”