Cameron faces the music on EU decision

European leaders on Tuesday put pressure on British Prime Minister David Cameron to expedite his country's exit from the European Union after its decision to leave rocked global markets.

Adding to the pressure, Standard & Poor's stripped Britain of its top-notch debt rating late on Monday following Thursday's referendum result.

Cameron, who had fought to remain in the EU and has said he will step down, told Parliament on Monday that he will not start the two-year countdown yet on leaving the bloc by invoking Article 50 of the Lisbon Treaty.

"Before we do that, we need to determine the kind of relationship we want with the EU, and that is rightly something for the next prime minister and the Cabinet to decide," he said.

However, in Berlin on Monday, German Chancellor Angela Merkel, French President Francois Hollande and Italian Prime Minister Matteo Renzi made clear that they want Britain to get down to business to avoid more uncertainty.

"There will be no informal or formal talks on the exit of Britain until an application has been filed to leave the European Union," Merkel said. Hollande told London to "not waste time".

Britain could have a new prime minister by early September, the ruling Conservative Party said on Monday, after Cameron started laying the groundwork for his successor to trigger the country's exit from the EU.

The government is under pressure to fill a vacuum left when Cameron announced that he would resign by October after Britain ignored his advice and voted to leave the 28-member bloc.

Triggering a leadership battle that could involve some of his closest advisers, he urged ministers to work together in the meantime.

Cameron also formed a unit, staffed by public servants, to help advise Britain on its departure and its options for a future outside the EU.

"Although leaving the EU was not the path I recommended, I am the first to praise our incredible strengths as a country," he told Parliament.

"As we proceed with implementing this decision and facing the challenges that it will undoubtedly bring, I believe we should hold fast to a vision of Britain that wants to be respected abroad, tolerant at home, engaged in the world."

Asked about the possibility of a second EU referendum, Cameron said the result of Thursday's vote must be accepted.