The EU's founding members have demanded the UK urgently invoke Article 50 and start the process of Brexit, reports Sky News.
Foreign ministers from the six original members attended a hastily arranged meeting in Berlin - with the UK not invited.
Speaking to reporters afterwards, French minister Jean-Marc Ayrault said it was a "matter of respect" that the UK did not "play cat and mouse" with its soon-to-be-former partners.
David Cameron said yesterday he would leave it to his successor to invoke Article 50, which will start the two-year negotiation of our departure.
A replacement is not expected to be in Number 10 until October - but pressure is mounting on the continent for swifter action.
Mr Ayrault said: "There is a certain urgency ... It is in Britain's interest and in the interest of Europeans not to have a period of uncertainty that would have financial consequences, and that could have economic and political consequences.
"Of course a new (British) prime minister must be appointed, that will probably require a few days but this is quite urgent."