Only one person in 10 claims to eat the recommended daily five portions of fruit and vegetables - the average is three portions a day.

The findings come in a poll conducted by Gallup on behalf of the BBC for its Fighting Fat, Fighting Fit campaign, which launches on Tuesday.

The results of the poll will be presented in the first programme of the campaign, Weight of the Nation.

The poll reveals the extent of the nation's knowledge of health issues but also highlights the lack of effort put in to maintaining a healthy lifestyle.

Weight gains

The poll showed that women are more likely than men to consider themselves overweight. Forty-five per cent of women thought they weighed too much compared with 33% of men.

The campaign launches on Tuesday

Women were also less likely to exercise than men. Overall, 37% of those surveyed said they did no exercise that would leave them out of breath in a typical week.

The Health Education Authority recommends up to 30 minutes of gentle exercise, such as brisk walking, every day. This can be split into segments of 10 or 15 minutes.

However, most people who responded knew that crash diets do not work.

Eighty-two per cent realised that the best way to achieve long-term weight loss was to make small changes to eating patterns over a year rather than go on a radical diet.

Improvements

Sixty-two per cent knew that it is not necessary to give up snacks such as chocolate completely in order to lose weight.

The poll also found that many Britons plan to improve their lifestyles in the new year, with 52% saying that they were likely or very likely to increase their exercise levels from 1 January.

Fiona Pitcher, the BBC Education executive who commissioned the campaign, said: "There's no such thing as a quick-fix diet.

"We want to encourage viewers and listeners to make small changes that suit them.