London/Brussels: The European Union (EU) President Donald Tusk on Thursday said Brexit could be reversed as leaders gathered for a Brussels summit amid growing confidence in a future without Britain.

Embattled Prime Minister Theresa May will make EU leaders an offer on the rights of expats after Britain’s withdrawal as she tries to convince them she still has a grip after her election meltdown.

But Tusk, who has repeatedly said Brexit benefits no one, especially not Britain, channelled former Beatle John Lennon as he became the latest in a series of EU leaders to suggest it was not too late to change tack.

“Some of my British friends have asked me whether Brexit could be reversed, and whether I could imagine an outcome where the UK stays part of the European Union,” Tusk told reporters.

“I told them that in fact the European Union was built on dreams that seemed impossible to achieve, so who knows?” the former Polish premier said.

“You may say I am a dreamer, but I am not the only one,” he added with a broad smile, quoting Lennon’s iconic song “Imagine.”

Newly-elected French President Emmanuel Macron and German Finance Minister Wolfgang Schaeuble both said last week that the “door was open” for Britain to remain in the EU.

Tusk insisted the remaining 27 members had a renewed sense of optimism about the bloc’s future after years of crisis and mounting anti-EU sentiment culminating in the Brexit vote.

Despite it being his 80th summit as premier or EU head, “never before have I had such a strong belief that things are going in a better direction,” he said.

“Our optimism should still be extremely cautious but we have good reason to talk about it,” Tusk said shortly before the summit opens at 1300 GMT.

In Brussels, security has been stepped up after Tuesday’s bombing at one of the city’s main rail stations by an Islamic State sympathiser, following attacks in Britain and France.

Macron won office as a committed European and has joined forces with German Chancellor Angela Merkel pledging to put the EU back on track to deliver prosperity and security after years of austerity and crisis.

But talks on issues including post-Brexit defence plans risk being overshadowed by concerns that a disastrous election has left May so enfeebled that Brexit negotiations will be hampered.

“There is an enormous insecurity among the Europeans: how long will she last? Has she got the majority to deliver?” a senior EU official said.

Over dinner, May is expected to fill in some of the blanks for the other EU leaders on Brexit.

It will be their first meeting since her Conservative party unexpectedly lost its majority in a June 8 election, leaving her in charge of a so-called “zombie government”.

May will outline her approach to the “hugely important issue” of reassuring EU expatriates about their future in Britain at a summit on Thursday which will be her first Brexit test since an election sapped her authority.

But her wings have been clipped — not only in Britain where voters denied her a majority in parliament, but also in Brussels where EU leaders will try to stop her from discussing Brexit beyond a quick presentation.

Instead, once she has left the room, they will continue their own discussion of Britain’s departure from the European Union, notably on which city gets to host two EU agencies being pulled out of London — a potentially divisive issue.

“My understanding all along is that this (expatriates question) is a hugely important issue for Britain and for the 27 that has been clear from the very outset of this process,” a senior British government source said.

“We want to provide early assurances, and it has always been our position that we want to outline our principles at this dinner and that is what we are going to do.” The source said Britain was “perfectly content” with the arrangements. Last week, one diplomat said May had tried to “hijack” the summit taking place on Thursday and Friday by drawing other leaders into wider discussions on Brexit.

Another British official said May would offer “new elements” in a paper to be published next week. There may be sticking points with Brussels, such as the cut-off date for EU citizens in Britain to retain rights under the bloc’s free movement rules and EU demands to preserve a panoply of rights in the future that may irk those keen to reduce immigrant numbers.

To show the “goodwill” her aides often refer to, May will have a separate conversation with European Council President Donald Tusk and hopes to have other one-to-one meetings. But it is not clear whether she will make any headway on the Brexit talks, which began in Brussels on Monday.

SOFTER TONE Weakened by an election she did not need to call, May has watered down her government’s programme to try to get it through parliament and set a softer tone in her approach to Brexit.

Yet her aims have held — she wants a clean break from the bloc, leaving the lucrative single market and customs union and so reducing immigration into Britain and removing her country from the jurisdiction of EU courts.

On Monday, her Brexit minister, David Davis, described the first day of Brexit talks to unravel more than 40 years of union as setting a “solid foundation” for future discussions.

On Thursday, her finance minister, Philip Hammond called for an early agreement on transitional arrangements to ease uncertainty that he said was hurting business.