The system for recovering cash from overseas patients who use the NHS is "chaotic", MPs have said as they urged the Government to "get a grip" on the issue.
In a damning report, MPs from the Commons Public Accounts Committee (PAC) said they were "not confident" the Department of Health is taking effective action to recover money from people who leave the NHS with unpaid bills after treatment.
It said the NHS was failing to identify patients who should be charged, while the Government was also failing to get money back from European countries where reciprocal agreements are in place.
In 2014/15, the UK recovered only £50 million from these countries but paid out £675 million.
The Government has a target to recover up to £500 million a year by 2017/18 from all overseas patients, though it is widely expected to miss this.
Some £289 million was charged to all overseas patients in 2015/16, though not all this will be recovered. At the moment, trusts collect only around half of the amounts they invoice.
In evidence to PAC, the Department of Health admitted that "very little happened" for more than 30 years after legislation was first introduced to recover money from overseas patients in 1982.
NHS hospitals are now being given "financial incentives" to do more to recover costs.
The new report calls on GPs to do more to help identify those patients who should be charged for NHS care following a referral to hospital.
And it points to a wide variation between NHS trusts in debt collection rates, from 15% to 100%. Just 10 out of 154 hospitals accounted for half of the charges to visitors from outside the European Economic Area (EEA) and Switzerland in 2015/16.
But the report warned that forcing all patients to show their passports or another form of identity, as introduced by some trusts, could penalise some people who do not have the documents but are eligible for free NHS care.
The report says the Department of Health must draw up an action plan by June to set out specific action for recovering more money.
Meg Hillier, Labour and Co-operative MP and chairwoman of PAC, said: "The Government's failure to get a grip on recovering the costs of treating overseas visitors is depriving the NHS of vital funds.
"Our committee has reported extensively on the financial pressures facing the health service and it is simply unacceptable that so much money owed should continue to go uncollected.
"This is a problem for the health service as a whole and work to put it right must be driven by central government.
"We are concerned that financial progress to date does not reflect meaningful progress with implementing the rules and the Department for Health and NHS have much to do if they are to meet their target for cost recovery."
In December, Freedom of Information responses from 104 trusts obtained by the Press Association revealed overseas patients have left the NHS with an unpaid bill of almost £30 million in just one year.
Patients who were not entitled to free treatment on the health service owed £29,530,378 in 2015/16.
Several NHS trusts provided figures for the past four years, showing they are now owed a backlog of millions of pounds.
In London, Barts is owed £10,340,322 from the past four years, while Imperial College Healthcare NHS Trust is owed £5,509,733.
Guy's & St Thomas' NHS Foundation Trust and London North West Healthcare NHS Trust are also owed around £5m each for the past four years.
A Department of Health spokesman said: "This Government was the first to put measures in place to make sure the NHS recoups money from people who are not eligible for free care.
"Some hospitals are already doing great work and the amount of income identified has more than trebled in three years, to £289 million.
"However, there is more to be done to make sure that if people are not eligible for free care, they pay for it.
"We will be announcing further steps very shortly to recover up to £500 million a year by the middle of this Parliament."
Dr Mark Porter, chairman of the British Medical Association (BMA), said: "It is important that those accessing NHS services are eligible to do so and that we recover the costs for treating overseas visitors.
"The systems to do this need to be practical, economic and efficient and must not jeopardise access to healthcare for those who need it.
"Any charging systems should not prevent sick and vulnerable patients receiving necessary care, otherwise there may be serious consequences for their health and that of the public in general."
Professor Helen Stokes-Lampard, chairwoman of the Royal College of GPs, said: "It is the role of GPs and our teams to deliver care to our patients, free at the point of need, regardless of their individual circumstances.
"We must stop perpetuating this idea that general practice should, in whatever way, assist with border control.
"Patients share information with their GP on the mutual understanding that it will remain confidential.
"We are very concerned that any process that undermines that crucial trust between doctors and patients will both deteriorate the doctor-patient relationship, and deter vulnerable people from seeking medical assistance when they need it."