Theresa May made an unexpected overture to EU leaders on Thursday night with a request for an “early” deal to protect expats’ rights after Brexit, as she attempted to come in from the cold at a summit in Brussels.

In a brief intervention on Brexit that elicited no response from other leaders, Britain’s prime minister offered an update on the legal situation in London and urged the EU-27 to promptly address the rights of individuals in negotiations.

“We need to give assurances to our citizens at an early stage of negotiations that they will have a right to stay [in whichever country they are living],” Mrs May said, according to one diplomatic note of proceedings. Moments later she left the summit room, leaving the EU-27 to hold a 20-minute discussion on Brexit process, confirming Michel Barnier as the union’s negotiator in future talks.

Although no leader responded directly to Mrs May’s remarks on citizens’ rights, Sweden’s Prime Minister Stefan Lofven later described it as “a very positive message”. A more sceptical European minister present at the summit said: “She’s trying. But she won’t get an answer.”

Breaking with usual practice at summits, Mrs May left without giving a full press conference, and her team made no prior mention of plans to give a Brexit update.

It’s a clear ambition that Britain does not want to complicate life for all these people . . . so I think that was a very positive message

Most leaders are keen to ensure the “acquired rights” of expats are protected — but work on a deal is expected to be tricky, covering detailed arrangements on residence, pensions, benefits and healthcare rights for expats and their children.

Mrs May’s low-key intervention came at the tail-end of a gathering where she tried to counter the idea that she has become a semi-detached EU member, by promising Britain would continue to tackle migrant flows from north Africa to Europe.

She also reassured fellow leaders from Latvia and Lithuania that Britain will fully support Nato efforts to deter Russian expansionism in the region. Separately Mrs May told Martin Schulz, European Parliament president, that she supports his bid to win a bigger role for MEPs in Brexit negotiations.

Enda Kenny, the Irish prime minister, said Mrs May gave a “formal, very short” update on Brexit after making contributions in various other areas that were “generally in line with what the European agenda is”.

The Irish premier said Mrs May told the room she would “like to have the question of UK citizens living in Europe and European citizens living in the UK dealt with in the early part of the [Brexit] discussions”. “There was not any response,” he added.

He noted that the EU leaders were “clear” that there would be no negotiations before Article 50 talks are triggered. “Her request today was that it would be early in the discussions and obviously at official level . . . I’m sure that is a matter that will come into focus when she moves Article 50,” he said.

Mr Lofven of Sweden, a supporter of as smooth and soft a Brexit as possible, said: “It’s a clear ambition that Britain does not want to complicate life for all these people who actually live in Great Britain, so I think that was a very positive message”.

There was no mention of more substantial issues — including the timeline for Brexit or need for a transition deal — either while Mrs May was present, or at the brief EU-27 discussion on Brexit that followed.

The prime minister had arrived in Brussels facing questions over official warnings from a senior diplomat that a final Brexit trade deal could take up to a decade to complete.

There is great scepticism in Brussels about claims by Brexit minister David Davis that exit talks and a new trade deal can be agreed within two years. The BBC reported on Thursday that Sir Ivan Rogers, Britain’s ambassador to the EU, had privately told the government that a post-Brexit UK-EU trade deal could take a decade to finish, and could still be scuppered during ratification.

That advice is consistent with the message from Whitehall in the run-up to the June referendum. A study published in 2015 suggested that complete detachment from the bloc could take 10 years.

Mr Kenny said he had made the point that “50 years of directives, legislation and so on would probably be very difficult to deal with inside a two-year period . . . It remains to be seen.”