During that time they have set the standard for "daytime TV", turning programmes that could have been mind-numbingly dull into something at least watchable and sometimes, dare I say, even entertaining.

Viewers have laughed and cried with them over the years – and sometimes cringed. Richard, in particular, became noted for his gaffes on air. He once asked a novelist, "If you were to write an autobiography, who would it be about?" His excruciating Ali G impersonation has since become part of TV folklore.

They made their debut together on ITV's This Morning in 1988, before switching to the afternoon slot on Channel 4 with their own show in 2001. They have now become so recognisable as "Richard and Judy" that it's hard to imagine one without the other.

Being in the limelight, though, has brought its share of unwanted attention. There was Richard's unfortunate brush with Tesco, when he was accused and acquitted of shoplifting, and Judy's embarrassing display of underwear at the National Television Awards, in 2000, when she was unaware that her top had slipped down while in front of the cameras.

But it's their down-to-earth attitude and the fact they seem to be "just like us" that has endeared them to the British public. Which is why, following their last scheduled show on Channel 4 tomorrow, viewers will probably follow them when they switch to UKTV.

Elaine Penn, features editor of TV Quick, says that Richard and Judy have changed the face of daytime TV.

"Working together and living together, it was as if they shared their private life with us and drew people in. They really broke through the barriers of the TV screen," she says.

"We love the chemistry they have between them and, as a result, presenters had to move away from what I remember as a more formal style and work on the kind of chemistry you see now with Fern Britton and Phillip Schofield and Adrian Chiles and Christine Bleakley.

"People felt they were seeing the real Richard and Judy, and I'm sure they were. And that's why we related to them. They seemed to have the same conversations we might have at home."

However, the couple are more than just a pair who indulge in light-hearted chat and gentle marital bickering. Both come from a news reporting background and met in 1982 while working on separate
news programmes for Granada TV, before getting married four years later.

It meant they weren't afraid to tackle challenging issues, including the furore surrounding Viagra.

In 1998, Richard and Judy were criticised for inviting three couples with impotence problems onto the show to test the new drug and report back.

A few years later they invited couples to have sex while wired up to monitors to find out if it was more efficient than a workout at the gym.

"They weren't afraid to do something different, something a bit 'out there' for daytime TV," says Penn. "But even when they were dealing with the more controversial subjects – like the Viagra show – they seemed to reflect the interests of us at home."

If the sex-themed shows were a bit too much for some people, the couple hit on a real winner when they started their book club. Although producers had initial concerns that it might be dull, the club has become a phenomenal success and is expected to move with them to their new TV home.

As well as being a big hit with readers, sales of books recommended on the show have gone through the roof. "Straightforward 'talking about books' shows have never really worked as far as getting people
to buy and read books is concerned, but the Richard and Judy Book Club has been the exception to the rule," claims a Waterstones spokesman.

Some books, such as The Lovely Bones and Labyrinth, were always likely to become bestsellers, but many others would never have sold as many copies had they not been recommended by the book club.

"The obvious example is Joseph O'Connor's Star of the Sea, championed so passionately by Bob Geldof on the show. In the end what Richard and Judy have done is tap into what booksellers have known for years – that the best way to get people reading books is to get them talking about books, and offering recommendations."

What the book club also shows, perhaps more than anything else, is Richard and Judy's innate ability to take something and make it accessible.