European Union leaders will Wednesday assess the damage from Britain's decision to leave the bloc and try to prevent further disintegration, as they meet for the first time without a British representative.
And as the shockwaves reverberate around British politics, Scottish First Minister Nicola Sturgeon is also expected in Brussels "utterly determined" to keep her pro-EU country in the club despite the Brexit vote.
At a tense summit that finished late Tuesday, the 27 remaining EU members agreed to give Britain some breathing space, accepting that it needs time to absorb the shock of the Brexit vote before triggering Article 50 that will begin the formal divorce proceedings.
Five days after Britain voted by 52 to 48 percent to leave the bloc, unleashing turmoil on global financial markets, EU President Donald Tusk said he understood that time was needed "for the dust to settle" before the next steps can be taken.
However, European Commission President Jean-Claude Juncker warned Britain did not have "months to meditate" and set a clear timetable for triggering Article 50 -- the EU treaty clause that begins the two-year withdrawal process -- after Cameron's successor takes office in early September.
"If someone from the 'Remain' camp will become British PM, this has to be done in two weeks after his appointment," he said. If they are from the Brexit camp, then it should be "the day after".
And German Chancellor Angela Merkel warned that London could not "cherry-pick" the terms of the exit negotiations.
Some in Brussels are concerned that giving Britain favourable divorce terms will spark a domino effect of others leaving the union, set up six decades ago to foster peace on the continent after World War II.
Cameron flew back to London after Tuesday's summit, as Sturgeon headed in the opposite direction to test the waters in Brussels for her country joining the bloc as a separate entity.
Scotland overwhelmingly backed "Remain" in last Thursday's vote, and the combative Sturgeon has said she was "utterly determined to preserve Scotland's relationship and place within the EU".
That may require a second referendum on Scottish independence, which failed in 2014, with Sturgeon saying that the Britain of that time "does not exist any more" following the Brexit vote.
Sturgeon will meet European Parliament President Martin Schulz, the heads of the parliament groups and Juncker, a commission spokesman said Wednesday.
The prospect of a second referendum on Scottish independence throws the future of the United Kingdom into question, as the entire British political establishment reels from the shock Brexit vote.
Scotland will draw up legislation for a new independence referendum to ensure it could be held during any negotiations for Britain to leave the EU, which would last a maximum of two years unless all EU member states agreed to extend them.
Cameron has rejected Sturgeon's initiative, saying Scots had already voted against independence in 2014, and the referendum would require the authority of the British parliament to go ahead.
"The last thing Scotland needs now is another divisive referendum," his spokeswoman said earlier.
Top of the agenda at Wednesday's EU summit will be how the remaining 27 members of the bloc can bolster unity after the shock of the British vote.
Cameron urged the EU leaders to consider reforming the rules of freedom of movement, which was one of the driving issues behind the surprise success of the "Leave" campaign and a concern that is shared by eurosceptics in other countries.
Merkel has called for a "new impulse" for the EU and stepped-up cooperation in areas including defence, jobs and competitiveness.
Meanwhile, both main political parties in Britain are in turmoil with the opposition Labour leader fighting for his political life and the ruling conservatives searching for a new leader after Cameron's resignation.
Labour leader Jeremy Corbyn vowed to fight on despite losing a crushing no-confidence vote among his party's lawmakers.
The new Conservative leader, who would also take over as prime minister, is expected to call a general election in order to firm up the party's mandate.
Meanwhile, on Tuesday thousands took to the streets of London, which voted to stay in the EU by a 60-percent margin, to protest the referendum result, waving EU flags and placards saying: "Stop Brexit" and chanting "Fromage (cheese), not Farage!".
Nigel Farage, head of the UK Independence Party and key figure in the "Leave" camp, told a jeering European Parliament on Tuesday that the joke was now on those who never expected Britain to leave the EU.
"When I came here 17 years ago and I said I wanted to lead a campaign to get Britain to leave the EU, you all laughed at me," he said. "But you are not laughing now."