Five days after Britons stunned the European Union by voting to quit the 28-nation bloc, key European leaders bluntly told Britain they wanted it to leave quickly - and not expect special treatment.
European President Donald Tusk said the bloc was ready to start divorce proceedings with Britain "even today" and the European Parliament called on Britain to initiate the departure process "as soon as possible."
In Berlin, German Chancellor Angela Merkel warned Cameron could not "cherry-pick" in the exit negotiations -- and there would be a price for Britain to pay.
The summit, starting mid-afternoon, takes place amid deep anger among the 27 other European leaders over Cameron's decision firstly to call the 'Brexit' referendum -- and secondly his handling of the campaign itself.
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That resentment has been compounded by fury over suspicions that Britain will now drag its feet over leaving, which would boost rising eurosceptic forces within the EU.
Cameron, who had fought to remain in the EU and has said he will step down, told his parliament yesterday that he will not yet start the two-year countdown on leaving the EU.
His successor is not expected to be appointed until September.
But European Commission chief Jean-Claude Juncker, speaking in a stormy session of the European Parliament where he was heckled by Brexiteer Nigel Farage, told Cameron to waste no time, adding: "No notification (of Article 50), no negotiation".
"It is we who must decide what happens, not just those who wish to leave the European Union," Juncker said, echoing comments yesterday from Merkel, French President Francois Hollande and Italian Prime Minister Matteo Renzi in Berlin.
Juncker said he had banned officials from holding "secret" talks with Britain.