A source close to Donald Tusk, the President of the European Council, has told CNN that European leaders have already begun the debate on whether to grant the UK an extension to Article 50.

The source said member states were still making up their minds about an extension and that there had not been a discussion with all members yet.

"What we are talking about is the UK leaving the EU. It's too important to take the risk [of a no deal by accident] for short-term political gains."

Donald Tusk, President of the European Council. Getty Images

The source added that Tusk does not believe a short extension will make a difference, if Theresa May's Brexit deal does not get approved by UK lawmakers.

"If they can't agree now, why would they agree in a few months? A short-term extension would increase the risk of a no deal by accident," the source said, adding it would be better to grant the UK an extension "of at least a year."

"They will have time to think it over, build a consensus and get back to the EU," the source said, adding that way it allows EU members to "get on with their business."

"In Brexit there are no winners," the source added. "Everything is about limiting the damage. A long extension might be the best way to do that."