Mothers-to-be who gorge on junk food may be more likely to give birth to a child with a sweet tooth, research shows.

The study, one of the first of its kind, suggests that a mother's diet during pregnancy, and even when breastfeeding, can affect her unborn child's taste for foods.

Researchers warned that women who use pregnancy as an excuse to indulge in fatty foods when "eating for two" may be inadvertently putting their children at risk of obesity in later life.

The finding comes as Britain fights the worst weight problem in Europe with almost a quarter of adults classed as obese. Child obesity rates have trebled over the last 20 years, with 10 per cent of six-year-olds and 17 per cent of 15-year-olds now obese.

By 2050, half of all primary school-age boys and a fifth of girls could be so overweight that their health is at serious risk.

Experts have warned that unless the Government acts now, an entire generation faces an old age blighted by heart disease, cancer, diabetes and other diseases brought on by obesity, with today's children dying at a younger age than their parents.

The latest research suggests that some of the roots of obesity can be traced back to the first days of life, with exposure to fatty and salty foods in the womb and through breastmilk having long-lasting effects on the development of those parts of the brain that control appetite.

Dr Stephanie Bayol (CORR), the study's main author, said: "Our study has shown that eating large quantities of junk food when pregnant and breastfeeding could impair the normal control of appetite and promote an exacerbated taste for junk food in offspring.

"This could send the offspring on the road to obesity and make the task of teaching healthy eating habits in children even more challenging."

Dr Bayol, of the Royal Veterinary College in London, looked at the effect of maternal diet on the appetite and weight of more than 300 rat pups.

Half of the mother rats were fed normal rat food, while the others were also given unlimited access to junk foods, including jam doughnuts, chocolate chip muffins, marshmallows and chocolate.

The baby rats exposed to junk foods in the womb or through their mothers' milk were more likely to be overweight ten weeks after birth, the British Journal of Nutrition reports.

Further analysis showed these creature ate more junk food themselves, and were particularly fond of treats high in fat, sugar and salt - the nutrients thought to activate the brain regions responsible for making food taste good.

Dr Bayol, whose work was funded by the Wellcome Trust, said the finding could also explain why some people crave fatty and salty snacks more than others.

She said: "Exposure to a maternal junk food diet during their foetal and suckling life might help explain why some individuals might find it harder than others to control their junk food intake even when given access to healthier foods in later life."

Fellow researcher, Professor Neil Strickland, said it was important that women were made aware of the potential consequences of "eating for two".

He said: "The Government is trying to encourage healthier eating habits in schools, but our research shows that healthy eating habits need to start during the foetal and suckling life of an individual.

"Giving children better school dinners is very good but more needs to be done to raise awareness in pregnant and breastfeeding women as well.

"Future mothers should be aware that pregnancy and lactation are not the time to overindulge on fatty, sugary treats on the misguided assumption they are 'eating for two'."