Health tourism from the European Union is costing the UK hundreds of millions a year, Brexit campaigners have claimed.
Analysis by the Vote Leave campaign indicates that the UK pays an average of £723 million a year more to EU countries for treatment of UK nationals than it receives back for treating their citizens in British hospitals and surgeries.
Figures released in response to a Freedom of Information Act request show that since 2007-2008, the UK has paid £6.18 billion to other EU member states for the treatment of British citizens in the EU, but received just £405 million from other EU countries for the cost of treating their citizens in the UK, a gap of £5.78 billion.
Vote Leave claimed the £5.78 billion could have paid for the construction of 17 new hospitals or trained more than 70,000 nurses or almost 15,000 GPs.
The Remain camp warned that the Brexit group's plans would mean Britons being forced to pay for emergency medical treatment they receive while on holiday in Europe.
Under the present system, British nationals are entitled to a free European Health Insurance Card (EHIC), giving them the right to access state-provided healthcare on temporary stays at a reduced cost, or sometimes free in EU countries, while citizens of other member states can access NHS treatment.
The Department of Health figures show that in 2014-2015 alone, the UK paid £667.4 million to other EU countries for the treatment of British citizens, but was able to recoup just £49.3 million for the cost of treating EU citizens in the UK, a deficit of £618 million - enough to employ an additional 4,458 NHS hospital consultants or to abolish prescription fees in England.
Vote Leave chairwoman and Labour MP Gisela Stuart said: "The UK has been getting short changed by the EU for years. We hand over £350 million to Brussels every week but get less than half of that back - with strings attached.
"On top of that, health tourism from the EU has cost us billions. This money could have been much better spent - it could have been invested to improve care for NHS patients.
"If we vote Leave we will be able to stop handing over so much money to the EU and we would be able to spend our money on priorities here in the UK like abolishing prescription charges and investing in the NHS."
In 2014, there were 23 million visits by EU citizens to the UK and 43.8 million visits by British citizens to the EU and Vote Leave conceded it could be expected that the scheme would cost more to the UK.
But Vote Leave cited 2014 figures showing there were 2.7 million EU citizens in the UK and just 1.1 million UK nationals in the other member states, suggesting the scheme should result in Britain receiving more money for their healthcare.
The Remain campaign group Britain Stronger in Europe said Ms Stuart's comments showed the Brexit group wanted to end the EHIC system.
Chief campaign spokesman James McGrory said: "I congratulate Vote Leave for their honesty in admitting that they would leave British holidaymakers out of pocket by forcing them to cover the cost of treatment in EU countries.
"Falling ill away from home is worrying enough, and the European Health Insurance Card allows British families to access the best available care without having to worry about the costs.
"Vote Leave clearly think that this policy is a price worth paying. But to leave Brits to face a massive bill on their sickbed miles away from home would be damaging and inhumane.
"The millions of British people who holiday in, or go on business to Europe every year are safer and better off thanks to our membership of the EU, while leaving would put travellers at risk."
Former health secretary and Labour In For Britain chairman Alan Johnson said Brexit would put the NHS "in serious danger" and dismissed the Vote Leave analysis.
"This is simply more desperate scaremongering from the Vote Leave campaign," he said.
"These figures are hugely misleading and ignore the fact there are far more British pensioners choosing to retire in European countries than EU citizens retiring here.
"As the governor of the Bank Of England and almost every reputable survey has pointed out, leaving the EU risks damaging our economy severely. It is upon a robust economy that a successful taxpayer funded health service depends."