The leaders of Germany, France and Italy agreed on the eve of the summit in Brussels that there could be no talks on Britain's relations with the group until after it has formally notified the European Union of its intention to leave by invoking Article 50 of the Lisbon Treaty.
Under EU rules, the UK would have two years to negotiate the terms of its divorce from the EU once it has triggered Article 50.
But Prime Minister David Cameron – who announced his plan to resign in the wake of the shock referendum vote – has insisted Britain will not pull the trigger until his successor is in place in September.
With England's disgraced football team returning from France after being dumped out of Euro 2016 by Iceland, Cameron heads to Brussels for an awkward encounter with his 27 counterparts.
A British government source said ahead of the meeting that Cameron will reiterate his position that beginning Britain's extraction from the EU is a job for his successor.
"He will want to encourage people to think about how both the UK and the EU needs to work now to make the best of the decision that the British people have taken," the source added.
Cameron will first sit down with EU President Donald Tusk, before the European Council meets later in the day.
Later, the British prime minister will "explain the situation" to his fellow leaders over a dinner, according to an invitation letter from Tusk.
German Chancellor Angela Merkel has been pushing for Britain to be given more time as the crisis tears through its political scene, with the end of 2016 being seen as the latest for Britain to trigger Article 50.
But she, French President François Hollande and Italian Prime Minister Matteo Renzi – who with Britain's exit make up the three largest economies in the bloc – all rejected London’s suggestion that it should have a "clear view" of what its future trade relationship with the EU would look like before initiating the divorce.
Merkel, Hollande and Renzi met on Monday in Berlin, and agreed "that there will be no informal or formal talks on the exit of Britain until an application has been filed to leave the European Union".
The German chancellor reiterated that view in an address to the German parliament on Tuesday, adding that Britain would not be able "cherry-pick" the parts of the European Union it wants once negotiations begin.
Merkel said she expected that Britain would want to maintain "close relations" with the EU once it leaves, though also signalling that it could not expect a business as usual approach.
"Whoever wants to leave this family cannot expect to have no more obligations but to keep privileges," she said.
Still a member
Britain's reluctance to start divorce proceedings has led some countries to think there may be space for a solution to keep it in the bloc, with Poland's ruling party chief suggesting Monday there should be a second referendum.
But other countries including France are taking a harder line, with Hollande telling Britain it should "not waste time".
The British government source suggested that Cameron will go to Brussels with the view that Britain is still a full EU member – despite its decision to leave, a position that may ruffle some feathers.
"I think he (Cameron) will want to make clear that as we approach these discussions the UK remains a full member of the EU as it currently stands, therefore it is down to the UK to respect its obligations but the UK should also continue to enjoy its full rights as a member too," the British government source said.
"I think he will want to underline the importance of the economic relationship both in our interests and the interests of the European member states," the source added.
On the second day of the summit on Wednesday Cameron will be left out in the cold when the remaining 27 EU states hold talks without him on the future of the bloc amid fears of a domino effect of referendums in eurosceptic countries.
(FRANCE 24 with AFP)