British men are getting heavier and joining the "Jim Royle generation", researchers in Oxford have warned.

The average British man piled on more than a stone in weight between 1986 and 2000, and experts predict the outlook is only getting worse.

Research from Oxford University showed the average man was 7.7kg (17lb) heavier in 2000 than he was in 1986. Women have not fared much better, with an average weight gain of 5.4kg (12lb) between the mid-1980s and 2000.

While men have put on weight due to poor diet and a lack of exercise, women have piled on the pounds by simply eating too much.

The research, funded by the British Heart Foundation (BHF), analysed changes in food consumption and body weight over a long time period.

Eating extra calories was enough to make men put on almost 5kg in weight, but they piled on even more pounds due to a lack of exercise.

NHS figures for 2008 in England, the most recent available, show that 25% of men were classed as obese, compared with only around 7% in 1986/7.

Dr Peter Scarborough, who led the latest study, said: "There could be a number of reasons for the reduction in exercise. One partial explanation could be that men spend more of their working lives sitting at desks now - manual careers are less common than they used to be.

"We looked at how much food was available over time, accounting for food that's wasted or thrown away. It's clear people are eating more, and today we're seeing a continued increase in the amount of food available."

The authors said achieving a balance in future should include "addressing the obesogenicity of the food environment".