Rates of obesity-fuelled cancers are now rising in successively younger age groups, a landmark study shows.

Experts said "shocking" levels of disease linked to growing waistlines across the globe threaten to reverse decades of progress in the war on cancer.

The Lancet study shows that rates of obesity-related cancers are rising faster in adults aged 25 to 49 than in older generations - despite the fact cancer is seen as a disease of old age.

The research, which examined 12 types of cancer linked to obesity, divided patients into five-year age groups from 25-29 to 80-84 years old.

In six of the main cancers - including bowel, pancreatic and kidney disease - it was found that the younger the age group, the greater the increase in incidence.

The major research used data covering more than half the population of the United States.

But British experts warned that trends in this country - where obesity rates are rising faster than the US - means there is a similar threat to Britain’s population.