Countess of Wessex gets on her bike for palace-to-palace 450 miles charity ride

"I haven't lost weight," the Countess of Wessex tells me, "but I have changed shape."

This royal transformation is the result of a demanding six-month training regime to prepare Sophie Wessex for a 450-mile cycle ride from the Queen's official Edinburgh residence, Holyroodhouse, to Buckingham Palace.

Sophie sets great store by physical fitness, but admits that at the age of 51 her new training programme has tested her to the limit.

"When I was going up yet another hill I just thought this isn't possible," she admits. "So I've probably surprised myself as to how far I've progressed and have proven to myself that yes, I'm getting off my backside and I'm going to do something."

The cycle ride, which will be spread over a week at more than 60 miles a day, is to raise awareness of the Duke of Edinburgh Award scheme in its 60th anniversary year.

And if Sophie wanted inspiration for the challenge she needed to look no further than her 95-year-old father-in-law.

"He's always remained fit," she says. "He realises that in order to retain his full physical faculty he has to get out there and make himself do things."

The countess is known to be a particular favourite of the Queen, who celebrated her 90th birthday earlier this year.

"She's fabulous. She still rides, she has dogs to walk, she's still very much engaged with all of her work.

"I think the work side of things helps keep not only a healthy mind, but a healthy body too."

But there seems little chance that Sophie's cycle ride will encourage the royals to copy Scandinavia royals who are regularly seen out and about on two wheels.

"A cycling royal? I'm not sure the lycra is the kind of thing we want to be getting into particularly quickly," says the Countess.

"If the traffic wasn't as bad as it is it might be a possibility, but I'm not sure that cycling and wearing a cocktail dress go together."