European leaders will decide on Wednesday whether to grant the U.K. another extension to its departure from the bloc, due to take place on Friday April 12.

The EU's 28 leaders, including British Prime Minister Theresa May, are heading to Brussels for an emergency summit dedicated to Brexit. This after May asked the bloc for a second delay to the U.K.'s departure.

The summit begins at 17:00 London time and May will formally present her case for requesting a short delay to Brexit until June 30, asking for the option to leave if a deal is agreed by the U.K. Parliament before then.

It's widely expected that the U.K. will be granted a longer, flexible extension with conditions attached, however, according to an invitation letter sent to EU leaders by European Council President Donald Tusk on Tuesday.

"I believe we should also discuss an alternative, longer extension. One possibility would be a flexible extension, which would last only as long as necessary and no longer than one year," Tusk said in his letter.

He called for a longer delay to avoid "the risk of a rolling series of short extensions and emergency summits, creating new cliff-edge dates."

Conditions that the U.K. could have to abide by, Tusk noted, would include no re-opening of negotiations over the withdrawal agreement (the Brexit deal) on offer. The U.K. could leave earlier than a newly agreed departure date if a deal is in place and Tusk reiterated that the U.K. could revoke Article 50 (the departure process) at any time.

A draft EU document circulated to diplomats ahead of the emergency meeting of EU leaders proposes an extension but leaves the date blank. It also notes that an extension cannot be used to undermine the EU or to start trade talks.