A no deal Brexit could see between 50,000 and 250,000 British expats return to the UK from the European Union, a leaked government memo has revealed.
The internal document, shared with Buzzfeed News, suggests government officials are preparing for a sudden rush of citizens to return home if Britain crashes out of the EU without a negotiated settlement.
Under the "worst case scenario" envisaged in the cross-Whitehall contingency planning document, about 150,000 people would return in the first year after the UK leaves the EU on March 29 — with around 30,000 coming back in the first three months.
Another 100,000 would follow in the next wave of the "Brexodus" the following year, according to the estimate.
The Department for Work and Pensions has a more optimistic assessment of the likely influx and is projecting that around 50,000 expats would return home if there is no deal.
The EU exodus could put a significant strain on public services, with around 40 per cent of returning expats expected to be be pensioners, placing pressure on the National Health Service and social care services.
The government has previously admitted it is cheaper to pay Spain and France to look after Britons than have them fly home.
Currently pensioners can have treatment reimbursed by the NHS under a reciprocal EU-wide arrangement.
However, expat retirees living in the EU using an S1 certificate, may no longer have their healthcare funded by the NHS after March 29.
The government warns that the European Health Insurance Card (EHIC) may not be valid for tourists and students on an Erasmus year abroad.
Currently around 1.3 million British citizens reside in countries across the EU. In the last five years, the number of British residents in Spain has fallen by 157,107, according to the country's National Statistics Institute.