London mayor Sadiq Khan has intensified his demand that Prime Minister Theresa May must respect the rights of EU migrants in the UK as she officially launches Brexit.
Mr Khan used a goodwill visit to Paris to press the PM to guarantee the status of some 3.3 million continental citizens living in Britain.
As Mrs May was poised to trigger Article 50, setting Brexit negotiations in train, Mr Khan said she must assure EU citizens in the UK about their future status.
Mr Khan said: "I'm pleased that the Prime Minister has today recognised the importance of reassuring EU citizens living in Britain who are understandably extremely concerned about their future.
"Today, Theresa May has a huge opportunity to give them a cast-iron guarantee that they can stay here after Brexit as she triggers Article 50.
"This would start negotiations with a powerful symbol of goodwill and both sides should give this assurance today."
Mr Khan, who timed his visit to Paris so he would be on the continent as Article 50 was invoked, said that both sides need now to focus on what is in their mutual Interest.
"I'm urging both sets of negotiators to make securing an interim deal their first priority, particularly for financial services.
"This will reduce economic uncertainty on both sides of the Channel while the negotiations unfold.
"I didn't vote for Brexit, but I am optimistic about London's future.
"My conversations with European and EU leaders this week have left me in no doubt that there is a good Brexit deal to be done if the Government approaches it in the right way, a deal that is in the best interests of London, Britain and the EU.
""However, striking this deal will be extraordinarily complicated and difficult and, like all Londoners, I am hopeful that the negotiators will act in good faith and agree a deal that works for everyone."