The European Union should stop waiting to see what the final Brexit deal is and "urgently" start planning for Britons who live on their territory now, a think-tank said on Thursday.
The rights of three million Europeans living in Britain has been a key issue in Brexit talks, but the situation facing around one million British expats in the other 27 countries is more uncertain, the Migration Policy Institute Europe said in a report.
The Brussels-based think-tank said the EU should streamline their systems for Britons who want to stay, and even allow them to register in friendly places like pubs to make the process less intimidating.
The lack of any final Brexit agreement has raised uncertainty but a roadmap for how EU countries should treat Britons living there was "urgently needed", MPI Europe said.
"Many EU countries have yet to begin planning for issues likely to affect their UK nationals after Brexit, with officials interviewed in a number of member states reporting they are unsure of whose remit these Britons will fall under," the report said.
While Britain had been "forced to show its hand" and spell out its plans for European expats during tense Brexit negotiations, the other 27 "have not been required to thoroughly think through" their plans.
Key steps should include avoiding requirements for retrospective documents proving past residence, MPI Europe said.
It also called for user friendly systems -- Britain has pledged to streamline its own systems for EU nationals who want to stay -- and to limit fees.
The think-tank also recommended "outreach strategies" such as updating official guidance, but also allowing Britons to register to stay in "a range of accessible and familiar settings, from libraries and pubs to hospitals and schools".
Without proper handling there could be a large "unauthorised population of Britons left without legal status" after Brexit, it said, warning that this could also encourage fraud.
The report comes as the EU raised fresh concerns about the treatment of its nationals after Brexit.
The European Parliament's Brexit coordinator Guy Verhofstadt said MEPs would be vigilant about the rights of EU citizens after Brexit, following a growing row over threatened deportations of people who moved to Britain from the Caribbean in the 1950s and 1960s.