European Union President Donald Tusk echoed rocker John Lennon's "Imagine" Thursday, June 22 as he said he hoped Britain might still stay in the bloc, AFP reports.

Speaking ahead of an EU summit in Brussels where Prime Minister Theresa May was due to brief leaders on her Brexit plans, Tusk suggested the process could still be reversed.

"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 added.

"You may say I am a dreamer, but I am not the only one."

Tusk's last line was a quote from "Imagine", the iconic 1971 ode to world peace by late former Beatle Lennon.

Britain stunned the EU when it voted to end its four-decade membership of the 28-nation bloc in a referendum a year ago.

But May's disastrous showing in elections on June 8 in which she lost her majority has sparked speculation that her Brexit plans may be watered down, or even reversed.

At the summit May is due to unveil a "generous offer" to resolve EU concerns about the rights of three million European expats living in Britain after Brexit.

Tusk meanwhile 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.