UPDATE 8-EU sets April 12 Brexit date if Britain fails to back deal

* EU leaders conclude May has little chance of success

* April 12, or May 22, loom as next Brexit deadlines

* UK parliament divided on how, when or whether to leave (Updates with conclusion)

BRUSSELS, March 21 (Reuters) - Britain could leave the European Union without a Brexit deal on April 12 if lawmakers fail next week to back Prime Minister Theresa May's agreement with Brussels, EU leaders said after a crisis summit in Brussels on Thursday.

With just a week to go until Britain risks lurching out into legal limbo at midnight (2300 GMT) next Friday, EU leaders gave May an extra two months, until May 22, to leave if she wins next week's vote in parliament. But she failed to convince the other 27 that she would succeed, prompting a frantic seven hours of talks to find a way to get Britain out without seeming to push.

The conclusion was a deal that suggested that Britain could, if May fails, come back and ask for a much longer delay. But this would be on the condition -- likely a major stumbling block -- that it takes part in elections to the new EU parliament on May 23. For it to do so, British election law says that would have to be announced six weeks beforehand, by April 12.

If it does not call an EU election, Britain will be out.

"The European Council agrees to an extension until 22 May 2019, provided the Withdrawal Agreement is approved by the House of Commons next week," the statement said.

"If the Withdrawal Agreement is not approved by the House of Commons next week, the European Council agrees to an extension until 12 April 2019 and expects the United Kingdom to indicate a way forward before this date for consideration by the European Council." (Reporting by Robin Emmott, Gabriela Baczynska, Elizabeth Piper, Richard Lough, Anthony Deutsch, Philip Blenkinsop, Giulia Paravicini, William James, Thomas Escritt, Jan Strupczewski and Alastair Macdonald in Brussels and Guy Faulconbridge and Kylie MacLellan in London Writing by Alastair Macdonald, Jan Strupczewski and Elizabeth Piper; Editing by Kevin Liffey and Alastair Macdonald)