Theresa May has sparked a new row with Brussels after she warned the UK would seek to limit the rights of EU citizens who come to Britain during the post-Brexit transition.
Speaking during the second day of her official visit to China, the Prime Minister said those arriving after the Brexit date of March 2019 could not expect to enjoy the same rights as those who came before.
Her intervention provoked an angry response from senior EU figures who insisted EU law, including the free movement of people, must apply throughout the proposed 21-month transitional period.
Guy Verhofstadt, the European Parliament's co-ordinator on Brexit, said the UK had to remain subject to the entire acquis, the accumulated body of EU legislation and case law, if the transition was to work.
"Citizens' rights during the transition are not negotiable," he said.
"We will not accept that there are two sets of rights for EU citizens. For the transition to work, it must mean a continuation of the existing acquis with no exceptions."
His comments were echoed by the parliament's vice-president, the senior Irish MEP Mairead McGuinness, who accused the Prime Minister of trying to appease critics on her own backbenches.
"I think what Theresa May is doing is trying to keep the Conservative Party Brexiteers online," she told BBC Radio 4's The World At One.
"There should be absolutely no misunderstanding here. The idea of the transition is to get us both to a place where we have a new relationship but in the interim, while the UK would leave the institutions, it remains within all of the acquis."
Ministers, however, said the EU's demands, which emerged in negotiating guidelines published earlier this week, contradicted the terms of UK's agreement in December with the remaining 27 member states.
In the Commons, Brexit Secretary David Davis told MPs: "In the report which we concluded and got agreement on in December, the European Union agreed that the end date of ongoing residents' rights will be March 2019."
Earlier, speaking to reporters, Mrs May made clear she was determined to fight the EU proposal when negotiations on the transitional arrangements begin .
"When we agreed the citizens' rights deal in December, we did so on the basis that people who had come to the UK when we were a member of the EU had ... made a life choice and set up certain expectations and it was right that we have made an agreement that ensured they could continue their life in the way they had wanted to," she said.
"Now, for those who come after March 2019, that will be different because they will be coming to a UK that they know will be outside the EU.
"This is a matter for negotiation for the immediate period but I'm clear there's a difference between those people who came prior to us leaving and those who will come when they know the UK is no longer a member of the EU."
Her stance was backed by pro-Brexit Conservatives. Former minister Sir Desmond Swayne said she was setting out a "perfectly proper negotiating requirement".
"One of the principle issues in the referendum campaign was gaining control of our borders," he told The World At One.
"If we are to have an implementation period if we are not to have control of our borders in the full sense during that period we would not have achieved then we haven't achieved what was set out as early as we would have wished.
"I think it is right and proper to have all of these arguments now."