European leaders have criticised the UK’s offer to EU nationals after Brexit – with one senior figure claiming it could “worsen the situation” for them.
European Council President Donald Tusk said the plan was “below expectations” while German Chancellor Angela Merkel said there had been “no breakthrough”.
Theresa May conceded there were differences between the two sides.
But the prime minister said those who had “made their lives and homes” in the UK would have their rights guaranteed.
She also suggested that while rights would be enforced by British courts, they could also be enshrined in international law if the agreement was included in the final treaty of withdrawal.
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Both the UK and the rest of the EU say they want to come to an arrangement to secure the status of the 3.2 million EU citizens in the UK and the estimated 1.2 million Britons living in EU countries.
Under plans announced on Thursday by Mrs May, the UK envisages giving all EU citizens the right to stay after the UK’s exit – due on 30 March 2019 – and granting those resident for at the least five years the same rights to welfare, pensions and education as UK citizens.
However, no cut-off date for the package has been specified by Downing Street and further details of the plans will not be released until Monday.
The offer has received a mixed response from EU leaders with some describing it as a “good start” but calling for more detail.
Speaking at a joint press conference with French president Emmanuel Macron, German Chancellor Angela Merkel said there was a “long way to go”.
“That was a good beginning but – and I’m trying to word this very carefully – it was not a breakthrough,” she said.
“We don’t want a wedge to be driven between us. We do want to make our interests very clear and if there is no guarantee for the full freedoms, then this exercise will have to lead to a situation where there are certain effects on the future relationship between the UK and the 27 member states.”
Mr Tusk, who represents the other EU 27 nations, said the EU would “analyse line by line” the UK’s proposals when they were published in full but his “first impression is that the UK’s offer is below our expectations and that it risks worsening the situation of citizens”.
And Joseph Muscat, the prime minister of Malta – who currently holds the rotating presidency of the EU – warned of people being “treated differently” depending on when they arrived in the UK.
Chris Morris, BBC News, Brussels
Both sides would like to get the issue of citizens’ rights wrapped up as soon as possible – it would be good for morale to get an early win, and they have more difficult issues to tackle.
But while there is a sense that progress can be made, there are still some tricky technical questions to deal with.
Which rights will be extended to immediate family members living elsewhere – to children in particular? And who will guarantee citizens’ rights in the event of any legal dispute? The EU has already insisted that the European Court of Justice should be involved; the UK insists that British courts should uphold the deal.
It is also not clear what the cut-off date should be for citizens to qualify for any offer that is agreed. The UK proposal suggests a date between March 2017 and March 2019 – although it is highly unlikely that the EU would be willing to accept a date that has already passed.
EU nationals in the UK currently have a right to permanent residence, granted after they have lived in the UK, legally and continuously, for five years.
The European Union has said EU citizens should continue enjoying the same rights as they do now on a lifetime basis, enforceable by the European Court of Justice. But the UK’s view is that British courts should have jurisdiction as they will be enshrined in UK law.
Mrs May said there had been a “very positive” discussion with other EU countries. She acknowledged differences over their enforcement but said she “remained of the view that this is a fair and serious offer”.
“Let’s be clear about what we’re saying. What we’re saying is that those citizens from EU countries who have come to the United Kingdom, those EU citizens who have made their lives and homes in the UK will be able to stay and we will guarantee their rights,” she said.
The PM said the issue would be one of the first to be discussed and she wanted an agreement as soon as possible.
In response to claims by the former chancellor George Osborne, in an article for the Evening Standard, that she had “blocked” calls for the UK to offer a unilateral guarantee of rights in the aftermath of last year’s referendum, she said that was “certainly not my recollection” of events.
Anne-Laure Donskoy, founding member of the 3million – which aims to protect the rights of EU citizens living in the UK – said the UK’s offer was “disappointing” and “really falls short of our expectations”.
“It is like a teaser this statement, it gives you general direction of travel potentially, but there are things in the statement that need to be unpicked.”
Labour leader Jeremy Corbyn urged the government to guarantee all UK-based EU citizens full residency rights, saying the current offer “doesn’t go far enough and leaves uncertainty for those who have been here for less than five years”.
“These are people who are working here and have families here – we have to end their uncertainty.”