This article has been updated to take account of new developments.
Rights for Britons residing in countries across the European Union and vice versa could be protected by a "separate deal" during ongoing Brexit developments.
The British government 's Brexit minister Steve Barclay has asked the European Union for its "formal views" on a proposal to safeguard citizens' rights, whether or not a deal is agreed.
The UK's Brexit minister Steve Barclay has written to the EU's chief negotiator Michel Barnier, after the British Parliament passed an amendment by Conservative MP Alberto Costa. Backed by citizens campaign groups and MPs across the political spectrum, it called for rights contained in the negotiated agreement to be ring-fenced even in the event of a no-deal Brexit.
Parliament's support for Costa's amendment forced a UK government U-turn. Prime Minister Theresa May had previously doubted that such a separate deal would be possible without a new EU mandate.
The3million group, a grassroots organisation lobbying for the rights of EU nationals in the UK, said its lawyers had found that May's comment over the legality of negotiating a separate deal was "incorrect".
May had told MPs on February 26 that without a new mandate, the EU did not have the "legal authority" to separate the issue of citizens' rights from the Brexit deal.
"This is a matter — unless it is part of the withdrawal agreement...good rights for citizens within the withdrawal agreement — for individual member states," she said.
The amendment specifically calls for a "joint EU-UK commitment to adopt part two of the withdrawal agreement on citizens' rights and ensure its implementation prior to the UK's exiting the European Union."
It received widespread support, with 141 MPs listed as signatories, and was passed unopposed during a parliament vote on February 27.
Referring to legalities surrounding the amendment, should it be approved by parliament, the3million said a separate deal concerning citizens' rights could be signed under Article 50 "as the only agreement, or even as an initial agreement while negotiations on the rest of Article 50 continue."
The European Council can revise its "nothing is agreed until everything is agreed" mandate at any time, the group said.
"The point of the amendment is to ask the European Council of 27 heads of state to change the existing mandate."
While the rights of EU and UK citizens remain somewhat confused, some of the EU27 published guidelines earlier this month on the immediate future of citizens' rights should the UK crash out of the EU without a deal on March 29.
But even with these guidelines, there are still no guarantees.