'Exercise has helped my depression'

But having shed stones in recent years, thanks to a gastric band coupled with sensible eating and plenty of exercise, most notably cycling, she's been fit for some time now.

On May 1 she embarks on #Challenge 57, a 1000-mile bike ride, cycling 57 miles a day (a mileage to match her age) from John O'Groats to Land's End, to raise £57,000 for Professor Robert Winston's Genesis Research Trust, specifically for research into miscarriage.

"I'm 57, I was born in 1957, and I want to do something big for that so #Challenge 57 was born," she explains of the challenge.

"I've been in constant training for the last 10 years so I keep it topped up, but in the last six months I've been pushing it some more. I'm doing hills that I couldn't do before. And I'm running two to three times a week."

She's also an enthusiastic gardener, although The Big Allotment Challenge, which she hosted, did not meet the hopes that it would be horticulture's answer to The Great British Bake Off, and hasn't been recommissioned for a third series.

Exercise plays a big part in her life, but she doesn't worry about injuring herself or her body wearing out.

"My core strength is very good at the moment, my legs are very strong. I do get tired, but then as you get older, you learn to use your energy wisely, so I have endurance. I can keep going all day but I'm not a racer."

The exercise also helps stave off the bouts of depression Britton has battled for years.

"I'm not on medication at the moment. I'm doing very well, and maybe upping the exercise has helped."

But she realises the depression could return.

"I'm fully expecting to have another episode. It takes a while to recognise it, but now that I'm experienced in it, I start to recognise the signs, usually when it's a bit too late.

"It's like in the distance you can see a hole in the road, and you know you're going to fall in it. The choice is fall in, walk round or jump over. In general, it's very hard not to fall in, so you go to the doctor and you get some help. The medication is so good.

"Feeling invisible and not looking forward to anything are two big signs. Those are mine. The family is very understanding because I can articulate it to them. "

Her fifth novel, A Good Catch, has just been published, a romantic yarn about the intertwined lives of two couples in Cornwall. It explores the subjects of class distinction, love unrequited, undetermined parentage - and body image.

One of the female protagonists, Loveday, is voluptuous rather than slender and not a conventional fashion-follower, but is an altogether more likeable and desirable character than her slim, well-groomed best friend, Greer.

Is this Britton's stand against the pressures women face to look slim and perfectly dressed?

"It wasn't an intentional rebellion but I can see why you would think that. I have a friend who is kind of Loveday to look at and she's just so gorgeous - men and women fall for her. She's got these fantastic jiggly bosoms. Everything about her is gorgeous. That's a good heroine to have.

"Women get it all the wrong way round," she continues. "Other women insist that women are one particular size and shape and that that's what guys like. Guys don't like that at all. They like personality, they want to know that you're going to jump on the back of a motorbike with them and cycle off up to the hills if you want to. They want you to be living life and enjoying life the way they do."

Britton still gets papped - often in an unflattering light, as when she's not working, she doesn't often wear make-up.

"There isn't a kind pap, but I'm grist to the mill because I never have make-up on and I look s*** and they take a picture. There you go," she says with a shrug.

Family remains her priority. She splits her time between Buckinghamshire and Cornwall, where they have a bolthole. Winnie, her 13-year-old daughter with Vickery, and Grace, 18, from her first marriage to TV executive Clive Jones, are still living at home, while twins Jack and Harry, 21, are at university.

Britton is contracted to write two more novels, although she likes keeping her toes dipped in the TV world, but not to the same extent as her This Morning days.

"I had a wonderful time doing it and you have to sometimes say you're very satisfied with what you've had and what you've done. I'm lucky to have done it.

"I love television. I still always want a foot in the door. However, I'm sensible enough to know that it will stop at some stage. "

Britton is one of those especially talented interviewers who assumes a cosy, comfortable rapport with interviewees, before slamming them with the killer question.

No one should forget that she was the one who coaxed former PM Tony Blair to say on her show Fern Britton Meets... that he thought it would have been right to remove Saddam Hussein, even if he had known beforehand that he had no weapons of mass destruction.

And in the run-up to this general election, you get the feeling that when she hears a debate or sees an inflammatory news story, she'd like to be right in there with the questions. She's she's been tweeting some of her frustrations.

"When I was listening to the news about Danny Alexander [chief secretary to the Treasury], not giving the name of the person who said across the Cabinet table, 'We'll look after the bosses, you look after the workers', I'd have loved to have properly interviewed him about that."

Britton tweeted: 'Why did nobody ask Danny Alexander this: Was it the Prime Minister?' 'Or: Was it the Chancellor? The Home Secretary?'

She admits she would like to have a chance to interview some of the main players in the forthcoming election.

"I'd ask Cameron not necessarily about policy, but about who he is. Whoever we're voting for, we need to know that we like them, that we trust them, that their ideas are based on a sane mind and a just and sincere mind.

"Politicians don't listen to us while they are in power, but as soon as they need our votes, they think we're stupid and are going to trust them. Well, we don't," she continues. " There's no sincerity with any of this electioneering this time. They are treating us like fools!"

This summer, Britton will be taking part in Channel 4's Time Crashers, a series in which 10 celebrities, including Greg Rutherford, Keith Allen and Kirstie Alley, are thrown into six different periods of British history, and have to try and live as though they're in that time.

She realises TV work may not be around forever, but Britton's adopting a healthy attitude to ageing.

"Instead of walking into age backwards, when you don't want to look because you'll see how you used to be, turn around and look into the distance of where you're going, and there's so much there to look forward to.

"I'm not ready for the scrapheap!"

:: A Good Catch by Fern Britton is published by HarperCollins on April 23, priced £12.99