BRUSSELS (Reuters) - European Union lawmakers want to tell Britons they can change their minds and stay in the EU after Prime Minister Theresa May triggers a two-year Brexit countdown on Wednesday.

FILE PHOTO - Participants hold a British Union flag and an EU flag during a pro-EU referendum event at Parliament Square in London, Britain June 19, 2016. REUTERS/Neil Hall/File Photo

The European Parliament is drafting a resolution to respond to May’s notice of withdrawal under Article 50 of the EU treaty. Senior lawmakers said it would stress London could still halt the process, as long as the other member states agreed.

The resolution text is not yet final but the intent is to strengthen the hand of those in Britain who want to halt Brexit.

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“We do not want to close the door to common sense,” Philippe Lamberts, Belgian co-leader of the Greens in the parliament, told reporters. A member of the Brexit team in the legislature, which will have to approve an exit treaty, Lamberts added: “There will be a reference to the revocability of Article 50.”

Elmar Brok, a member of the team from German Chancellor Angela Merkel’s Christian Democrats, also said there was such a reference in the draft resolution, to be agreed by party leaders on Wednesday and put to a vote in the legislature next week.

Insisting Britain can U-turn enters hazy legal territory.

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It defies May, who says the process cannot be halted despite Brexit opponents’ hopes of a new referendum or British parliamentary vote. And although EU officials disagree with May and have said the process can be stopped, with the consent of all states, they do not welcome Brussels lawmakers’ bid to revive the issue.

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Donald Tusk, the European Council President who will receive May’s letter on Wednesday, has said since last June’s referendum vote to leave that he was sure the other 27 member states would agree to let Britain stay if it had a change of heart.

But he will make no mention of that this week when he gives the EU’s response to May by issuing draft guidelines for the Brexit negotiations, EU officials said. Even governments most reluctant to see Britain go have little appetite for the further upset and uncertainty a British U-turn would have.

The bloc’s chief negotiator, Michel Barnier, had tried to discourage lawmakers from making explicit reference to halting the exit, parliamentary officials said, and had insisted that it include a reference to any cancellation of the Brexit process requiring the unanimous approval of all 27 other member states.

Aides to Barnier declined immediate comment.

The question of whether unanimity would be needed has divided legal opinion in Brussels but EU officials said on Tuesday the prevailing view was that it was necessary.

Last month, former prime minister Tony Blair called on Britons to “rise up” and try to block Brexit if they could.

But that may no longer be entirely in British hands. One senior EU diplomat said of Blair’s campaign: “This bus has left.”