Many more expat UK pensioners rely on European healthcare under reciprocal healthcare agreements than UK-based European pensioners rely on the NHS.
While 70,000 retired Brits use Spain's health system, 81 Spanish pensioners are registered as covered by the NHS.
Across the European Economic Area (EEA) there are 145,000 UK expat pensioners registered, compared with 4,000 EEA pensioners registered to use the NHS.
The figures were obtained after a BBC Freedom of Information request.
Citizens of the EEA - EU states and Iceland, Norway and Liechtenstein - can get public healthcare in all EEA states, which is ultimately claimed back from their home country.
The Department of Health figures show that the UK and Spain have the biggest disparity in numbers of pensioners covered by the reciprocal healthcare agreement, as of December 2016.
And while 43,000 British pensioners were registered to use the French health service, only 201 French pensioners were registered as covered by the NHS. In Cyprus 12,000 British pensioners are covered by the health service, but fewer than five Cypriot pensioners were covered by the NHS.
Britain paid £674.4m to other EEA countries to cover expat British citizens' health costs in the 2014-2015 financial year, while it claimed back £49.7m to pay for EEA citizens' treatment in the UK.
Questioned about the small numbers of Spanish pensioners that were choosing to retire in the UK in November, Department of Health civil servant Chris Wormald told a Public Accounts Committee hearing on reciprocal healthcare: "We are not the retirement place of choice."
When Britain leaves the EU, these arrangements would cease to apply if it also left the EEA and would need to be renegotiated as part of any exit deal.
Switzerland, for example, is not a member of the European Union but has negotiated access to EEA reciprocal healthcare arrangements.
Professor Catherine Barnard, Professor of EU law at the University of Cambridge, says that much will depend on the Article 50 Brexit negotiations and any transitional arrangements.
If the terms are not as good as the current ones, she said, pensioners may no longer get the same access to public healthcare in these countries.
"Of course it then becomes expensive for older people to get health insurance, and so it may be they feel obliged to return to the UK," she said.
'Seeking best possible outcomes'
While some British pensioners who have been living abroad for more than five years might still be granted access to public healthcare under an EU directive, this would still require they have health insurance and sufficient income not to be a burden on the public funds of the member state in which they reside.
Shadow Health Secretary Jonathan Ashworth said: "The government needs to urgently tell us if it's their intention to maintain those reciprocal healthcare arrangements after Brexit."
A spokesman for the Department for Exiting the EU said: "The prime minister has been clear that we will work to ensure the best possible outcome for the British people.
"Healthcare arrangements will depend on reciprocal agreement by other countries. We are about to begin these negotiations and it would be wrong to set out unilateral positions in advance."
Caroline Abrahams of Age UK said it was an "anxious time" for retired expats: "We know that reciprocal healthcare arrangements are a vital safety net and people are likely to have made the decision to live overseas based on their existence. Without that safety net many may feel they have no choice but to return."
For the Lib Dems, healthcare spokesman Norman Lamb said the reciprocal deal must be protected adding: "It would be ludicrous if the government, in what appears to be a zealous fixation on reducing migration at all costs, pulled us out of the EEA without due consideration of the security that these deals provide to British pensioners in Europe."