Cabinet ministers face a visit from TV fitness guru Mr Motivator if they fail to keep up their new year's healthy living resolutions, the Prime Minister said today.

Gordon Brown said he would be encouraging MPs to sign up to the exercise instructor's new GMTV campaign 'Get Motivated'.

Mr Motivator, best known for his appearances in colourful leotards on GMTV in the 1990s, burst into Downing Street to promote the campaign following the launch of the Government's own anti-obesity initiative earlier this week.

Mr Brown told him: "I'll tell the Cabinet Ministers that you're after them - you're coming!"

The Prime Minister revealed that he enjoyed getting up early to exercise and also told how he encouraged his children to take walks over Christmas by setting up treasure hunts at the end.

He greeted Mr Motivator, real name Derrick Evans, by saying: "It's a joy to have you here; I've just broken from my run."

Asked whether he enjoyed exercising in the morning, Mr Brown said: "It is the best time, as long as you can actually fit it in."

Mr Motivator said he had been away from GMTV for 10 years and during that time, "waistlines have got bigger".

The Prime Minister said he believed it was important to give people incentives to get fit.

"During Christmas we took my children on walks - that's a great thing to do - and we had treasure hunts at the end of the walks to encourage them," he said.

"I keep telling my children - five fruits, five vegetables a day. I think it's really important.

"And if you start very young, you do it continuously. But if you don't start young, it's sometimes very difficult to persuade people to do it."

In an interview with the Observer, Mr Brown admitted on Sunday that his New Year's resolution was to get fitter.

He said: "I will never be able to be back to being the sprinter that I used to be but I want to be fitter. What would I do a mile in? It's a bit more than it used to be."

On Saturday, Health Secretary Alan Johnson launched the Government's anti-obesity drive, saying he wanted children "to live longer, healthier lives".

The Change4Life campaign aims to "kickstart a lifestyle revolution for every family" by promoting healthy eating and exercise. The initiative involves companies such as Coca-Cola, Mars and Nestle.