Robbie Coltrane makes a rare TV appearance in Jack Dee’s acerbic BBC2 sitcom, Lead Balloon (Tuesday, June 28). The 61-year-old Scottish actor, best known for portraying Fitz in Cracker and Hagrid in the Harry Potter films, plays convict Donald, an unhinged lifer who takes Rick Spleen (Dee) hostage in prison.

TV&Satellite Week magazine caught up with him to find out more…

You rarely appear on TV these days. Why did you say yes to Lead Balloon?
“I am a huge fan of the series and, don’t let him hear me say it, of Jack Dee. I’ve always loved that style of comedy – people like Jack or Tony Hancock or Basil Fawlty, who make absolutely no effort to be liked. It’s such a contrast to the ingratiating style that so many comedians adopt.”

Which comics do you mean by that?
“I’m naming no names but, in a lot of TV comedy, people are trying to be liked, which I find very irritating. What’s great about Rick Spleen is that he doesn’t do that. He’s cowardly, dishonest and disillusioned with life, which is what makes him so funny. All the best comedy is about the distance between who you are and who you’d like to be – that’s universal. Like Rick, we’ve all had moments when our behaviour has fallen well short of our expectations of ourselves.”

How does Rick end up in prison in this episode?
“His wife urges him to do a comedy workshop in a prison because she has a social conscience. Rick just sees it as a way of earning a fast buck. And while he’s there, my character, Donald, takes him hostage.”

What’s his reaction to being imprisoned by a knife-wielding killer?
“Rick is under threat, so his cowardice immediately comes to the fore. He has to befriend this psychopath and wheedle his way into his good books but, as always, fails miserably.”

How do Rick and Donald get along when they’re thrown together?
“At first, Rick is a total crawler to Donald. He pretends to be much nicer and more selfless than he is, but is perpetually caught out. Donald has been lied to and horribly let down throughout his life, and instantly smells a rat with Rick. That’s where the comedy comes from, and people will recognise that situation. We’ve all tried bluffing, but the fear of being caught out generally stops us from behaving as badly as Rick does.”

How does the hostage situation pan out?
“Donald eventually persuades Rick to behave properly. It is one of the rare occasions on which Rick is actually honest. To paraphrase Doctor Johnson, being in a room with a psychopath does focus the mind.”

As a two-hander, the episode is quite theatrical, isn’t it?
“It is like a play – there is a distinct progression in the relationship between Rick and Donald. But don’t say it’s like a play or no one will watch it. They’ll say: ‘I’m not watching a play – I’d rather watch Celebrity Underpants.’ Actually, the sad thing is that someone will now commission Celebrity Underpants. But remember, I own the idea.”

How did you go about researching the part of Donald?
“I’d read a lot about psychopaths when I did Cracker. One of their enduring characteristics is they can change in an instant from friendly to vicious. They call them ‘violent’ mood swings for a very good reason.”

Why do you think the Harry Potter film franchise has been so hugely successful?
“There is so much in the books and films. People always ask me why they’re so popular, and it’s because JK Rowling has very carefully not made them fashionable or trendy. No one is playing on the Wii or listening to an iPod. The stories are about friendship and trying to be true to yourself and be popular – the stuff we all go through as teenagers.”

Do Harry Potter fans approach you in the street?
“Because I’m bearded up as Hagrid, kids generally don’t recognise me. I very much appreciate that anonymity – especially when you see what happens to Alan Rickman, who plays Snape. He gets kids hissing at him in airports! But when kids do recognise me, they go all doe-eyed, which is great.”

Did you ever get stopped by fans of Cracker?
“Quite the opposite – people would move away from me in supermarkets. They thought I was about to take them into the frozen fish section and psychoanalyse them.”