Ravens is aiming to impress with solo show

She said: "I think people who decide to go to the show will get more than they bargined for.

"It's a full look at impressions, why people enjoy them and how they are created, how you squeeze the comic juice out of a character.

"We also take a look at impressions in history and whether there is any evidence of people doing them before the mass media came into being."

Jan's show features a host of recognisable faces and she is keen for audiences to see the process she goes through to build the caricatures.

She said: "Impressions are created in one of two ways for me. Either somebody leaps out at you and begs to be done, like Ellen McArthur - the way she seems so frightened of everything and the way that could be applied to everyday domestic situations. Those are the ones that just tickle me.

"Otherwise, with characters that are topical I just have to sit down and learn them. I start looking at their vowel sounds, the pitch and the tune of their voice and the shape of their teeth and their mouth.

"I remember when Dead Ringers trasferred from radio to TV somebody said, 'That's going to be a big jump', but doing an impression is about a charachter's whole physicality. It's the same whether you're doing it in a studio or in front of a camera."

Jan said because she is doing impressions of real people, the content of her material is something she has to consider carefully.

She said: "If I'm given a sketch that I think is unecessarily cruel, then I'm not going to do it, especially if it's specifically about somebody's physical appearance.

"But then it's difficult because if you're going to do an accurate impression of Cherie Blair for example, you're going to have to do the mouth. It's important to be accurate because one of the things people enjoy about impressions is recognising the person you are doing."

But Jan keeps her characters strictly professional. She said: "I have absolutely no problem stopping when I come off stage.

"I've had taxi drivers tell me they've had Jon Culshaw from Dead Ringers get in the back and entertain them the whole way home. All power to him for just keeping going when he gets off stage. I'm more likely to just sit there quietly."

The tour, which is playing more than 50 dates across the country, is something of a departure for Jan as a performer.

She said: "It's hardcore. You get off stage and then you have to dismantle the set and drive to some motorway service station ready to travel to the next venue in the morning.
"It's really quite hectic, an endless problem-solving excercise, but the staff at the venues have been absolutely brilliant.

"The show is quite hard work. You're on stage for two hours and it's just you. There's no point where someone else comes on and you can just go off and get a cup of tea. If you want to have a laugh, find out about what I do and learn to do impressions yourself then come along."

Greenwich Theatre, May 21, 7.30pm, £15 (£12.50), 020 8858 7755, greenwichtheatre.org.uk, DLR: Greenwich