Scotland and Northern Ireland, both of whom voted to Remain, flagged moves to break off a suddenly disunited kingdom in order to stay in the EU.

More than 60,000 Londoners petitioned the mayor to declare the city independent so it could remain in the EU.

And the Irish Department of Foreign Affairs reported a "high volume of calls" to the embassy asking about Irish passports.

Economists warned of years of dampened corporate investment, employment and consumer spending.

Britons shared grim memes about a newly-devalued pound, which hit a 30-year low as international markets weighed the probably economic effects of Brexit and found a lot not to like.

The Bank of England was forced to intervene, saying it would "take all necessary steps" to prevent an uncontrolled collapse in the pound.

The stock market also slumped, with banks including Lloyds, Barclays and Royal Bank of Scotland losing a fifth of their value by Friday lunchtime.

Rating agency Standard & Poor's warned Britain would lose its last remaining triple-A credit rating, saying it was "untenable" in the face of Brexit.

Meanwhile, leadership speculation distracted both Labour and the Conservatives.

David Cameron's vow to resign by October fired the starting gun on the race to succeed him, with prominent Leave campaigner Boris Johnson trying to position himself as a progressive, Europe-friendly voice – an irony not lost on protesters who booed him out of his Islington home.

And a group of Labour MPs rose in open rebellion against Jeremy Corbyn, whom they blamed for not doing enough to energise the Labour base for Remain.

A motion of no confidence in Mr Corbyn was tabled by Labour MPs Margaret Hodge and Ann Coffey, though he was expected to survive the move with the support of the unions.

According to polling, almost two-thirds of Labour supporters were for Remain, while only 42% of Conservative voters were. Less than a third of the eventual Remain vote came from Conservatives.

Shadow chancellor John McDonnell told Channel 4 he expected a general election to be called as soon as the new prime minister took office in the autumn, which would require killing off a recent law imposing fixed parliamentary terms..

Meanwhile, rumours spread of big businesses already making plans to quit for the continent.

The BBC reported that US investment bank Morgan Stanley had a strategy to move 2000 staff out of London to either Dublin or Frankfurt – though the company denied the story.

Airbus announced it would "review UK investment strategy, like everybody else will".

Labour's former foreign secretary Margaret Beckett said she feared major firms including Rolls Royce, train maker Bombardier and car giant Toyota would leave the UK.

Some desperately speculated on Friday that the government, or parliament, might foil Brexit with a new referendum or by simply declining to act on the will of the people expressed in the vote.

Outside Number Ten, David Cameron insisted "The will of the British people is an instruction that must be delivered".

However he then declined to deliver it himself, saying it would not "be right for me to try to be the captain that steers our country to its next destination".

For Britain to leave the EU, the government must formally activate 'Article 50', a hitherto-unused treaty power that sets off a two-year period of negotiation with the continent over the terms of divorce.

Mr Cameron said it was for the next prime minister to take the decision about when to trigger Article 50.

The man considered most likely to be that PM, Boris Johnson, said there was "no need for haste". 

"Nothing will change over the short term except that work will have to begin on how to give effect to the will of the people."

Part of the reluctance to leap into negotiations was the reaction of Northern Ireland and Scotland to the result.

Both had voted to Remain in the EU – Scotland by a heavy margin.

Scottish first minister Nicola Sturgeon said a new independence plebiscite north of the border was "highly likely". It would be "democratically unacceptable" to drag Scotland out of the EU against its will, she said, after 62 per cent of Scots backed Remain.

And Northern Ireland's Deputy First Minister Martin McGuinness called for a new poll on a united Ireland. His region receives considerable 'peace money' subsidies from the EU. However the call from Sinn Fein's McGuinness was rejected by both the pro-British first minister and the Irish prime minister.

Within England, regions who had come out for Leave such as Cornwall sent querulous demands to the Leave camp seeking reassurance that their European subsidies would be refunded by Westminster.

Johnson directly addressed those in the UK and overseas "anxious" about the consequences of Brexit.

He specifically addressed young Britons, who had voted strongly to Remain in the EU.

"This doesn't mean the UK will be in any way less united nor any less European," Johnson said, denying the result was an isolationist "pulling up a drawbridge".

"We are part of Europe," he said. "Our children and grandchildren will continue to have wonderful future as Europeans.

"Britain will continue to be a great European power. We can find our voice in the world again."

He promised a more prosperous future for the UK by taking back control of laws and policies, saying Britain would continue to be a "powerful, liberal, humane and extraordinary force for good in the world."

Conservative MP Michael Gove promised a calm and consensual approach to implementing the Brexit process.

The mission was to "secure the best possible terms for Britain" in the upcoming negotiations with Europe, predicting a "gradual divergence" from the EU.

But the President of the European Parliament, Martin Schulz, said the EU would not let the UK re-join the single market.

"Leave is leave", he said.

Angela Merkel invited the French, Italian and European leaders to talks on Brexit next week.

Nigel Farage continued to celebrate achieving the apotheosis of Euroscepticism, which he had dubbed 'Independence Day'.

He called for the day to be made a national holiday, and predicted the next countries to have EU exit referendums would be Denmark, Sweden, Austria and Italy.

But he was attacked for apparently backing down on a key Leave campaign promise just hours after the vote.

Asked if he would continue to support the promise that leaving the EU would free up £350 million to spend on the NHS, Mr Farage said "no I can't and I would never have made that claim… it was one of the mistakes I think the Leave campaign made".

One of the Leave campaign buses was emblazoned with the slogan "We send the EU £350 million a week, let's fund our NHS instead".