Britons are under-reporting how many calories they consume by around 50%, finds a study of Behavioural Insights Team (BIT).

While scientific and economic data indicate that an adult consumes 3,000 calories, official surveys show calorie intake of 2,000.

BIT was quoted by the Financial Times as saying: “Such a large underestimate of calorie intake could misinform the policy debate and lead to less effective strategies to combat the current national obesity crisis.”

"Reductions in physical activity do not provide a realistic explanation for the rise in obesity rates over the last 40 years."

The part-privatised government agency raised questions on the official statistics over the last 40 years that indicated a sharp dip in calorie consumption even when obesity levels have surged.

Obesity levels in the UK are growing quickly and is stretching the finances of the National Health Service in treating obesity-related illnesses such as type 2 diabetes.

NHS chief Simon Stevens has been urging the government to take steps to cut down obesity levels.

Stevens has also been critical of the food and drink industry for using excess sugar in their products.

The government had stated that it intends to roll out sugar tax on sugary carbonated drinks in 2018 and a strategy to cut down obesity levels in children.

The food and drink industry, on the other hand, has been pointing out the official data, which indicate consumption of sugar levels have come down and obesity problems are growing because people are exercising less.

BIT report, however, rejects this explanation, stating that “reductions in physical activity do not provide a realistic explanation for the rise in obesity rates over the last 40 years.”

BIT director of health and co-author of the paper Michael Hallsworth was quoted by the Financial Times as saying: “Strategies to reduce obesity should focus on reducing calorie consumption. Our analysis shows that it’s unlikely that calorie intake has dramatically decreased in recent decades. Instead, it seems we are reporting our consumption less accurately.”

The organisation has urged the Government Statistical Service to seek new and improved methods so that people do not under-report their calorie intake.