ALAN Davies has something to point out about his career. He has done stand-up and drama and TV comedy since he first started out in the late 1980s, but he is still most famous as Jonathan Creek, the magician’s assistant who can solve seemingly unsolvable mysteries, and as the panellist on QI who is made to look like he knows nothing about anything. In other words, he says, he is both the cleverest person on TV as well as the biggest idiot.

The truth, says Davies, is that he’s neither of those things. People who meet the actor and comedian for the first time sometimes expect him to be as clever as the genius magician or as stupid as the quiz show dunce, but the reality is somewhere in the middle. “I very much navigate between them,” he says, “but sadly for me the person on QI is not as far away from the truth as I would like. I really don’t know much about anything, but I’m still curious and I like a laugh.”

This is one of the reasons he keeps saying yes to Jonathan Creek, which is returning for a special this Christmas. The show, which is written by David Renwick, who also created One Foot in the Grave, first appeared in 1996 and has never really gone away, popping up occasionally for a few episodes or the odd special when Renwick thinks of an idea.

Renwick thinks of the ideas, apparently, by lying on the carpet face down until inspiration comes to him and, bizarre as it might seem, Davies says it always works and it has certainly produced a clever and spooky episode this year. It centres on a house, Daemons’ Roost, that was once owned by a sorcerer named Jacob Surtees who could apparently summon the powers of Hell to terrorise and subjugate his victims, and Davies says it has all the familiar ingredients.

“It obeys all the conventions of the genre,” he says. “It feels familiar, but David combines greatly comic plots with dark tragic plots and is able to obey all the conventions of comedy and tragedy in a way that’s unusual. It’s also never been dependent on any gimmicks in the shooting, or on-screen graphics or whatever the latest thing is, which you might think in a few years ‘oh yes, they used to do that didn’t they?’”

Davies has been appearing in Creek since 1996, but says the experience has changed for him. When he started out, he was a young single man; he is now 50 and married with three children, which can make the process of making the show difficult.

“I don’t think anyone in their right mind would enjoy the hours that you do,” he says, “and I don’t understand why everyone has to do 12 hours. But it’s just presented to you as a fait accompli – this is how you make programmes. But why? It’s ridiculous. Why do we have to do six 12-hour days in a row?

“When I started doing Jonathan Creek, I was young and single and didn’t have any kids, I didn’t care, but now I look back at those crews and how many of them have families broken up and divorces – I think it’s inhumane to make people work these hours. So I really do hate the hours – I’m not joking.”

However, Davies accepts there is no prospect of anything changing – they will just hire someone else he says – and is grateful for a role that he almost never got – the BBC hierarchy wanted Nicholas Lyndhurst or Hugh Laurie for Creek and the producers had to fight to get Davies. This, he says, is typical of the management-heavy BBC, with the same happening to Sandi Toksvig when the producers of QI suggested her as Stephen Fry’s successor.

“The decision to replace Stephen became one that was shared by numerous people and the producer John Lloyd told me he wanted Sandi Toksvig to do it – she was his number one pick,” he says. “But he had six meetings at the BBC before they eventually said ‘all right, we’ll give her one year’ and of course immediately she slotted in perfectly.”

With Toksvig's arrival as the presenter, Davies’ role has slightly changed – he used to be the fool to Fry, but he’s now the teacher’s pet to Toksvig. But he says the core of the show has not changed. “It is thoroughly researched and a huge amount of work goes on,” he says. “There’s no point going in with a few jokes ready and waiting for your chance to get your lines in – in other words, it is not Mock the Week, it is a really collaborative, off the cuff conversation and it’s more fun for it.”

This year’s series is QI’s – and Davies’s – 16th but he still has other projects on the go, including a DVD release of his most recent stand-up tour Little Victories. “For a while, I wondered if it might be a young man’s game and that after a while you get replaced by a younger version of yourself appearing at the Edinburgh Festival or wherever,” he says, “and then I realised that’s not the case and returning to people whose comedy is getting deeper and richer and more personal and funnier is better."

QI, December 22, BBC Two, 10pm; Jonathan Creek, December 28, BBC One, 9pm. Little Victories is out now on DVD.