London, Jun 28 (IANS): British Prime Minister David Cameron is heading to Brussels on Tuesday to address a summit on why the UK voted to leave the European Union (EU) as a result of a historic referendum held last week.

Cameron will meet the European Commission President, Jean-Claude Juncker, and the European Council President, Donald Tusk, before a working dinner with his counterparts from the 27 other member states, at which the verdict in the referendum will be the only item on the agenda, The Guardian reported.

However, he will not attend talks between the leaders of the other 27 EU member states at breakfast on Wednesday.

The credit ratings agency Standard and Poor’s announced on Monday night that it was stripping Britain of its prized AAA credit rating, underlining the risks that may lie ahead.

Cameron is standing down after last week's referendum went against him. The prime minister campaigned for the UK to remain a member but has insisted that the result must be accepted.

Conservative MPs have announced that it would fast-track the process of replacing the prime minister against the backdrop of turmoil in financial markets.

Candidates hoping to succeed Cameron will be jockeying for position - with former London Mayor Boris Johnson and Home Secretary Theresa May widely seen as frontrunners - with nominations for the Conservative party leadership race set to open on Tuesday.

Speaking on Monday, he said a special unit within government was being set up to lay the initial groundwork for leaving the EU.

He said that it must be up to his successor - who will be elected by the start of September - to decide how to proceed and precisely when to give formal notification of the UK's intention to leave the bloc.

Under EU rules, once this happens, the UK would have two years to negotiate the terms of its divorce from the EU - unless the remaining 27 members unanimously agreed to extend the process.

It must also decide the shape of its future trading relationship with the EU.