European Union leaders want Great Britain to leave the alliance immediately rather than wait to open negotiations until the fall when British prime minister David Cameron says his successor will undertake the job of exiting.

At issue is the implementation of Article 50 – the mechanism by which a member-state can exit the EU.  The EU is looking into the possibility of triggering the process itself rather than waiting for Great Britain.

USA Today:

Top diplomats from France, Germany, Netherlands, Italy, Belgium and Luxembourg — the EU's six founding nations — met in Berlin on Saturday for hastily arranged talks following the stunning vote to leave the political alliance.

"The shock of the vote is still sitting deep, but these are also days where not all the answers are ready," German Foreign Minister Frank-Walter Steinmeier told reporters. “It’s totally clear that in times like these, one should neither be hysterical nor fall into paralysis,” he said.

European Parliament President Martin Schulz told the Guardian that EU lawyers were examining if the triggering of Article 50 of the Lisbon treaty — the launch process that will enable the U.K. to leave — could be sped up. As it stands, only the U.K., as the departing nation, can trigger Article 50. Once it does, exit negotiations will last for two years.

France's Foreign Minister Jean-Marc Ayrault said there was urgency, "so that we don’t have a period of uncertainty, with financial consequences, political consequences.”

Prime Minister David Cameron, who backed staying in the EU, wants his successor to negotiate the process. He has vowed to stand down by October.

That uncertainty has already had consequences for Great Britain.  Moody's has downgraded the U.K.'s outlook:

In a fresh sign of problems, Moody’s Investors Service downgraded the U.K's. outlook from “stable” to “negative” on Saturday. Moody's said the referendum result “will herald a prolonged period of uncertainty for the UK, with negative implications for the country’s medium-term growth outlook.”

Moody's said it believed that "many investment and spending decisions are likely to be put on hold" during the period of the U.K. withdrawing from the EU and negotiating a new trade agreement with the bloc.

Since it's never been done before, we can expect chaos and uncertainty to dominate.  The U.K. is going to have to deal with bitter, resentful Europeans who are going to want to make Great Britain pay for defying their will.  And given the enormity of the task before them, negotiators for the U.K. are going to be under the gun to achieve terms at least as good as those they had when they were part of the EU.

Most economists are predicting a recession in Great Britain because of Brexit.  That, too, may speed the negotiations to a conclusion so that some sort of stability can be established that will settle the markets and allow the economy to recover.