Lazy summer holidays are leading to a significant drop-off in schoolchildren’s fitness levels and hampering efforts to reverse the UK’s physical inactivity epidemic, new research suggests.

The study from the ukactive Research Institute found British schoolchildren are losing 80 per cent of fitness gained during term time due to sedentary school holidays. More than 400 children taking part in the My Personal Best Challenge developed by Premier Sport were found to have experienced significant drop-offs in their fitness levels post-summer break, as well as a marked increase in BMI.

As a result, the study’s authors say the government’s promise of a £500m cash-injection into school sport through the sugar levy should also be used to provide incentives for children and parents to be active over the summer to counter this drop-off.

“The research we are presenting shows for the first time that the inactivity problem in the UK stems from an inactive summer time,” said ukactive research director and lead author Dr Steven Mann, who presented the findings last month at the annual American College of Sport Medicine conference.

"Schools and activity providers are doing a fantastic job to increase fitness levels during term time, but the evidence shows that we need to focus our efforts on ensuring that the summer months are active months for all children.”

Previous research has shown that, only half of seven-year-olds are meeting recommended physical activity guidelines of 60 minutes per day, with bad habits often being forged through sedentary early years. There has been increased focus among policymakers on how to reverse the situation, amid warnings that children’s inactive lifestyles are a ‘ticking time-bomb’ for the NHS.

Further research from ukactive has highlighted how excessive screen time on computers, TVs and iPads is one of the biggest causes of sedentary behaviour among children during school holidays. A recent poll found that almost nine in ten UK parents feel tablets and smartphones are adding to Britain’s youth inactivity crisis, with ukactive calling for an urgent rethink of how children are engaged with physical activity beyond the school gates.

"This scientific evidence means we can be much smarter when we invest in children's fitness, using meaningful and measurable interventions to drive improvement,” said David Batch, chief executive of Premier Sport.

"One of the key findings was that this measurement is entirely scalable and as a result, central government, local authorities, school governors, headteachers and individual class teachers can now finally use evidence to base their investment decisions upon.

"A larger study is already underway funded by Camden and Islington Council, but we must use this information to progress from simply spending more money just to return children to their starting point each academic year.”