In what can be classed as a triumph for all calorie-counting single women, obesity experts have found that Britain's females pile on the pounds when they cohabit with their partners.

They begin consuming man-sized portions, rich foods and wines, and they skip gym sessions to indulge in romantic meals at restaurants instead.

Dr David Haslam, a GP who co-authored a review in the medical journal The Lancet, analysed the growing girth of women in relationships. He said the "odds were stacked against being thin".

"Men are very bad for women really. From a woman living independently to living as part of a couple, the change in eating will affect women greater."

Modern living required far less physical exertion for women, he added, compared with their grandmothers. The sharing of housework between the sexes may also have led to women's added weight.