- Video report by ITV News Political Correspondent Carl Dinnen
Prime Minister Theresa May has said she will fight efforts to give EU nationals full citizens' rights if they come to the UK as late as the end of 2020.
But it comes as a leak shows her Brexit team estimate new trade deals won't cover the economic hit of curbing migration.
Leaked government documents, obtained by BuzzFeed, showed Brexit analysis prepared for the Department for Exiting the EU suggested immigration reforms will outweigh the potential positive impact of a US trade deal.
The European parliament's Brexit coordinator also swiftly rejected Mrs May's claim.
Guy Verhofstadt told the Guardian: "Citizens’ rights during the transition is not negotiable. 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."
Mrs May had addressed the issue on a three-day trade mission in China as she criticised a proposal on EU citizens' rights which emerged in negotiating guidelines agreed by the EU27 earlier this week.
It contradicts last month's agreement that rights would be assured only to those settling in the UK before Brexit day in 2019.
"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."
Mrs May also rejected speculation she might seek to extend the expected two-year transition period after the official date of Brexit on March 29 2019 to three or more years.
"People are saying 'Oh we're secretly negotiating for three years'. No. We're not," she said.
The PM said she understands voters wanted a change in the UK's relations with Europe when they backed Leave in the 2016 referendum.
And she repeated her promise to deliver on Brexit, noting that the 17.4 million Britons who handed victory to Leave "did not vote for nothing to change when we come out of the EU."
Asked if she believes in Brexit "hand on heart," May replied: "Yes."
Her comments will be seen as an effort to allay concerns among Tory MPs over Chancellor Philip Hammond's suggestion that Britain's relationship with the remaining EU will change only "very modestly" after Brexit.
Cabinet members including Boris Johnson have warned that the UK will lose the main advantages of Brexit if it remains bound by the trade rules of the single market and customs union.
And Ukip's Nigel Farage coined the phrase Brino - Brexit in name only - as he accused the Government of preparing to water down withdrawal
Mrs May rejected the suggestion that she believes voters can be offered a form of Brexit that effectively leaves the UK-EU relationship unaltered.
"What we're doing now is doing the job that the British people asked the Government to do, which is to deliver on Brexit," she said.
"They want us to do that. But in doing that, they did not they did not vote for nothing to change when we come out of the EU."