Brussels (AFP) - Britain "may never" trigger the formal divorce process with the EU despite last week's referendum in which the country voted to leave, EU diplomats said Sunday.

"My personal belief is they will never notify" the EU about their intention to leave, a senior EU diplomat said on condition of anonymity.

A state leaving the EU must formally notify the European Council of all 28 EU leaders under Article 50 of the 2007 Lisbon Treaty, setting the clock ticking on a two-year period for Britain to negotiate its divorce.

"We want London to trigger Article 50 now, to have clarity. I expect, as we can't force them, for them to take their time," the diplomat added.

"And I would not exclude, it's my personal belief, that they may never do it."

The official did not specify if he believed Britain would avoid it by holding a new referendum, or simply dragging out the process to extract a better divorce deal, but said all such decisions were up to London.

Cameron has said he will resign by October and that it is for his successor to launch the process and lead the negotiations.

Despite growing pressure from EU leaders, Cameron was not expected to trigger Article 50 at an EU summit on Tuesday, another senior EU official said.

Britain's EU partners believed the notification should come by Christmas at the latest.

"There cannot be any kind of negotiation with Britain before there is a notification."

Meanwhile the EU had received "thousands" of emails from Britons since Friday saying they were unhappy with the result, including some from people who had voted to leave the EU and were now regretting it.

"It's the first time after a decade of hate mail from Britain, we are flooded with love emails," said the diplomat.