Britons find it hard to resist "super sizing" meals to extra large portions, according to a survey published today.
Almost 70% of people are tempted to upgrade our meals, particularly when the additional cost is just a few pence, the research found.
The poll, by weight-loss and weight-management specialists LighterLife, also revealed that 77% felt the average plate size had increased in the last decade.
Mandy Cassidy, psychotherapist for LighterLife, said: "The research highlights how cheap food, a lack of awareness of appropriate portion size and junk food promotions are tempting British people to over-eat."
More than 80% of consumers confessed to regularly carrying on eating even when feeling full, and 54% admitted they feed themselves and their children man-sized portions.
Professor Iain Broom, medical director of LighterLife and an expert on obesity, said: "Obesity continues to be a significant issue for many individuals and is set to cost the NHS significant amounts of money.
"In extreme situations, by choosing the wrong foods in the wrong quantities it can lead to a dramatic reduction in life expectancy."
:: The OnePoll survey was based on the response of 2,000 consumers in July.