UKIP leader Nigel Farage declared June 23 "our independence day" and called for the Prime Minister to immediately stand down in response to voters' rejection of his passionately-argued advice to stick in the EU.

But Foreign Secretary Philip Hammond told Sky News the Government's job now was to get on with implementing the decision while "protecting the economy and doing all we can to get the best outcome for Britain".

After the pound suffered one of its biggest ever plunges in value, the Bank of England said it would take "all necessary steps" to ensure monetary and financial stability in the wake of the Brexit vote.

In a political earthquake which sent shockwaves around the world, the referendum called by Mr Cameron produced an unexpected victory for Leave by a majority of 52% to 48%.

Sterling slumped to lows last seen in 1985, losing more than 10% against the US dollar at one point, as traders responded with panic to the prospect of the UK quitting the European Union after 43 years.

Mr Hammond did not rule out an emergency summer budget to respond to the damage the Government expects the Brexit vote to inflict on the UK economy. Ahead of the referendum, Chancellor George Osborne warned that a Leave vote might result in higher taxes, lower public spending or both, and Mr Hammond said that the Government's fiscal consolidation programme would now become "more difficult".

The Foreign Secretary said the markets' response to the vote showed that "we don't control everything", adding: "We can't just ignore the economic facts. We have to respond to them. We will have to look at the situation, see where the market settles, see what the immediate impact on the economy is and decide how best to proceed."

With votes counted in all 382 polling areas, Leave received 17,410,742 votes (51.9%) against 16,141,241 (48.1%) for Remain .

With Mr Cameron expected to address the nation from Downing Street before financial markets open, Labour said he should "seriously consider his position". Bank of England Governor Mark Carney is expected to make a statement after the Prime Minister.

As polling stations closed at 10pm on Thursday with polls still predicting a Remain victory, 84 pro-Leave Tories - including Boris Johnson and Michael Gove - handed a letter to Mr Cameron urging him to stay on as leader whatever the result of the referendum.

But as Leave built an increasingly unassailable lead as the night wore on, with victories in the Tory English shires, Labour strongholds in the North, Wales and Midlands, others in his party raised questions about Mr Cameron's future.

Long-standing Eurosceptic John Redwood suggested Tories should wait to see if Mr Cameron was willing to "implement the public will" after a Leave vote.

Mr Redwood said the PM should bring in talent from the Leave side to build "a new government to bind the country together". And Conservative backbencher Jacob Rees-Mogg said a general election in the autumn was "not impossible".

Influential backbencher David Davis said there was no need for the Prime Minister to go now, suggesting he could stay on for a "couple of years" but should put someone else in charge of negotiations on a new relationship with the EU.

Shadow chancellor John McDonnell said the Bank of England may have to intervene to shore up the currency. Mr Cameron would now be "a hostage" to his pro-Brexit MPs, who will make sure they seize "key positions", he said, warning that "ordinary people must not pay the price" of the Leave victory.

The Remain side was buoyed during the night by strong performances in London, Scotland and Northern Ireland.

But its fate was sealed by poor results in many of Labour's traditional strongholds in the north of England, including Sheffield, where Mr Farage hailed a narrow victory for Leave as "amazing". In a surprise result, Birmingham voted to Leave by the slimmest of margins.

The result in Scotland is certain to create massive pressure for a second independence referendum. Former Scottish National Party leader Alex Salmond said he was "quite certain" that an effort to drag Scotland out of the EU against its will would lead to the invocation of a manifesto promise to stage another ballot if there was a "significant and material" change in circumstances from the 2014 vote.

First Minister Nicola Sturgeon said Scotland had delivered a "strong, unequivocal vote" making clear that "the people of Scotland see their future as part of the European Union".

The results sparked calls from within Labour for a change in direction, with Bassetlaw MP John Mann saying that the strong showing for Brexit in former heartland areas showed the party was "out of touch" with traditional voters who were "sick to death" with what they were being offered.

Mr McDonnell acknowledged it was clear "people don't think we've been listening enough" and suggested Labour should reconsider its stance on freedom of movement.

Speaking at the Electoral Commission's main counting centre in Manchester, Vote Leave chairman Gisela Stuart said the Brexit vote was "our opportunity to take back control of a whole area of democratic decisions".

All political leaders should now "reflect on whether they have accurately gauged the people's desire to govern themselves", she said.

The German-born MP said a calm cross-party effort was now needed to implement the voters' decision "in the best long-term interests of this country". And she broke into her native tongue to assure other EU nations that Britain would remain an "open, welcoming" country which would continue to co-operate with its former partners.

Leaders of the European Commission, Council and Parliament were due to give their initial response at a press conference in Brussels, amid speculation that a leaders' summit scheduled for Tuesday may be brought forward to deal with the decision.

Senior Labour backbencher and former Europe minister Keith Vaz said the EU should call an emergency summit to deal with the aftermath of the vote, which he described as "a crushing, crushing decision ... a terrible day for Britain and a terrible day for Europe".

Senior Leave campaigners including Andrea Leadsom and Liam Fox urged the Prime Minister to wait before invoking Article 50 of the Lisbon Treaty, which starts the process of negotiating a new relationship for the UK with Europe, with a two-year deadline to reach a deal.

In their letter, the pro-Leave Tories told Mr Cameron: "We believe whatever the British people decide you have both a mandate and a duty to continue leading the nation implementing our policies."

As well as Mr Johnson and Mr Gove, the signatories included Cabinet-level Brexit backers Chris Grayling, Theresa Villiers, John Whittingdale and Priti Patel.

But notable absences included former Cabinet ministers Iain Duncan Smith, Owen Paterson, Cheryl Gillan and David Jones, along with the chairman of the backbench 1922 Committee Graham Brady and influential MPs including Mr Davis and Bernard Jenkin.

Labour's Jonathan Ashworth said the Conservative Party was "utterly preoccupied with leadership infighting rather than the future of the country", adding: "This letter cannot unsay what senior Tory politicians have been telling us for weeks - that the British people simply cannot trust David Cameron."

Senior Labour figures sought to cast the result as a protest against the effects of austerity as well as an expression of desire to leave the EU. Mr Mann said there must be urgent reform of the application of the EU's free movement regime in the UK.

Some 72.2% of the 46,500,001 eligible voters turned out at polling stations, said the Electoral Commission. The total turnout of 33,568,184 was just short of the highest ever participation in a UK general election, in 1992.