David Cameron is to face leaders of other EU states for the first time since the referendum vote for Brexit, as he travels to Brussels for what is likely to be his last European Council summit as Prime Minister.
Government sources said that the PM would use the potentially awkward meeting to urge the other 27 leaders and EU institutions to take a "constructive" approach to negotiations over a new relationship with the UK.
But he will resist pressure for an early start to the two-year talks process, insisting that it is a matter for his successor as PM to decide when to issue formal notification of Britain's intention to leave the EU under Article 50 of the Lisbon Treaty.
Despite calls for an "immediate" move to withdrawal negotiations from European Commission president Jean-Claude Juncker, the new PM may not be in place until as late as September 2.
Health Secretary Jeremy Hunt has suggested Britain could hold another vote on the leaving the EU.
The next Prime Minister should be allowed to "negotiate a deal" with Brussels that the public can have a say on through a second referendum or a general election.
In an article for The Daily Telegraph he said: "We must not invoke Article 50 straight away because that puts a time limit of two years on negotiations, after which we could be thrown out with no deal at all. So before setting the clock ticking we need to negotiate a deal and put it to the British people, either in a referendum or through the Conservative manifesto at a fresh general election."
Mr Cameron will attend a working dinner devoted to the consequences of the referendum vote, which has sent shockwaves through Europe's political establishment and sent stock markets tumbling across the continent.
But he has not been invited to the second day of the summit, when the other 27 leaders will hold informal discussions on the stance the EU should take towards the UK's demands.
Brexit standard-bearer and bookies' favourite as next PM, Boris Johnson, said on Monday he expected Britain to be able to impose points-based controls on EU migrants coming to the UK, while retaining the right for its own citizens to work and settle elsewhere in Europe and to access the single market.
His proposal for informal talks to sketch out a blueprint for future UK/EU relations before the invocation of Article 50 were rebuffed by leaders of Germany, France and Italy, who said there would be no negotiations "before an application for exiting the EU has been submitted to the European Council".
The summit comes a day after ratings agency Standard & Poor's downgraded the UK by two notches from its top AAA grade to AA, warning that victory for Leave had led to "a less predictable, stable and effective policy framework".
A Government source said Mr Cameron would use the meeting to "encourage people to think about how the UK and EU make the best of the decision of the British people".
He will make the point that, until the withdrawal negotiations are complete, the UK remains a full member of the EU entitled to the full rights of membership.
After telling the House of Commons on Monday that it was vital for Britain to maintain the "strongest possible" economic links with the EU, Mr Cameron will tell fellow leaders that a good economic relationship is in the interests not only of the UK but of all the remaining member states.
The source dismissed suggestions that Mr Cameron's exclusion from Wednesday's meeting amounts to a snub, saying: "We respect their right to have these discussions."
MEPs were due to discuss the fallout from the referendum in a special session of the European Parliament in Brussels.
Business Secretary Sajid Javid will hold a round table discussion with industry figures over the impact Brexit will have on their companies and sectors.