A very sprightly 80-year-old, Sidney tells me he puts his success down to his empathy with his characters. "I feel everything they feel," he says. "If I'm writing about a character who's in pain, I'm in physical pain. If he's happy, I'm happy." Goodness knows what happens when he writes a sex scene.
Sidney has never been abducted by aliens (at least to his knowledge - I didn't have time to hypnotically regress him) but he reckons there's something to it. "I wouldn't be surprised if the government's covered it up," he says.