The NHS could face a bill of £1 billion every year if retired British expats who are currently cared for in Europe need to receive their treatment in Britain, a new report has suggested.
If all the British pensioners who currently receive health care in other countries through European Union (EU) agreements had to return, caring for them would require the NHS to spend an extra £1 billion a year, according to a report from the Nuffield Trust.
The health charity said that this is twice the amount that is currently spent for them to receive their care abroad.
Under the EU reciprocal 'S1' scheme, British pensioners have the right to go to any other EU member state and receive the same health care rights as the local population.
The agreement currently protects around 190,000 British pensioners - costing the Department of Health around £500 million a year.
Meanwhile, if the NHS needed to care for those who currently receive care abroad, it would need a significantly higher number of hospital beds - the equivalent to two new hospitals, the authors said.
Brexit negotiators should try to secure a deal which would mean that expats still receive care in the country they reside in, they added.
The report also highlights how health and care services are dependent on EU migrant workers.
The authors say that the NHS depends on nurses from the EU "to prevent the serious problem of under-staffing from getting even worse".
Meanwhile, social care faces a shortfall of as many as 70,000 workers by 2025/26 if net migration from the EU is halted after Brexit, they added.
Report author Mark Dayan, policy and public affairs analyst at the Nuffield Trust, said: "The NHS and social care were already under pressure from tight funding settlements and growing staffing problems well before the EU referendum last year.
"But if we handle it badly, leaving the EU could make these problems even worse, given the potential impact on both the strength of the UK economy and the supply of overseas staff to both health and social care services.
"It is possible that extra funds could be found for the NHS from any cancellation of Britain's EU membership fees - but whether or not these benefits will outweigh the significant staffing and financial costs Brexit may impose on already stretched services remains to be seen.
"That depends largely on the NHS being recognised as a significant priority as we enter some of the most important negotiations in Britain's history."
Mark Porter, chairman of council at the British Medical Association, said: "These figures are a stark reminder that with the NHS at breaking point, politicians must keep the health service and its patients at the forefront during Brexit negotiations and reduce the impact that leaving the EU will have on health and social care across the UK.
"Not only might NHS resources fall, but existing chronic staff shortages could be worsened as half of the 10,000 EEA doctors working in the NHS are considering leaving the UK. This would seriously impact patient care across the country and increase what are often already unacceptable delays for treatment.
"It is vital that the next government ensures long-term stability for the NHS by granting permanent residence to EEA doctors working in the UK; maintains the current working time regulations; protects life-changing medical research which benefits from European funding; and ensures that leaving the EU will not delay the UK's access to vital pharmaceuticals."