The camp in favour of Britain's exit from the European Union (EU) was leading by four percentage points over the Remain camp with over 70 per cent of results declared in the referendum today as a BBC forecast said the results were for 'Brexit'.
The "too-close-to-call and knife-edge" prediction of the opinion polls seemed to hold true as Leave grabbed 52 per cent of the vote to Remain's 48 per cent with over 70 per cent of the results in.
The BBC said that the trends indicated that the Remain side could not regain from this position and the 52-48 per cent count in favour of Brexit is likely to be the final verdict of the British voters.
Far-right UK Independence Party (UKIP) leader Nigel Farage declared victory much earlier, saying: "Dare to dream that the dawn is breaking on an independent United Kingdom… June 23 will be our Independence Day."
The vote - which saw an extremely high turnout of around 72 per cent - reverses the public verdict back in 1975, when the UK voted to remain a member of then European Economic Community, which later became the EU.
The argument swiftly moved to the future and what happens next in the event of a Brexit vote. While the result of a referendum is not legally binding on the UK government, David Cameron has repeatedly promised that the will of the people will be accepted.
In the immediate aftermath, Britain will remain a member of the EU and nothing will change instantly. The British Prime Minister has pledged to activate Article 50 of the 2009 Lisbon Treaty as soon as possible if the result of the referendum is to leave the EU.
The Article begins negotiations with the EU's 27-member states for the UK's exit. That process could take two years or longer, with scope to extend the negotiation period if all parties agree. Once Article 50 has been triggered, the only way back into the EU is with the agreement of all member states.
Earlier, Gibraltar had been the first of the 382 local counting areas to declare, voting overwhelmingly in favour of staying in the EU, as had been expected.
The territory on Spain's southern tip voted 95.9 per cent "Remain", against just 4.09 per cent – 823 votes – for Brexit. In terms of broad trends, the vote reflected a very divided country with north-east England and Wales backing Brexit, while Scotland and Northern Ireland appear to have opted for Remain.
The markets reacted to the uncertainty with the pound surging as the polls closed last night, before falling dramatically to its lowest point since the 1980s.
Unlike at a General Election, the results in individual areas do not count as it is the overall number of votes cast for one side or the other that will determine the outcome. The side which wins over 50 per cent of the votes at the end of the count would be considered to have won.
The final national result is to be officially declared by the UK Electoral Commission's chief counting officer Jenny Watson from Manchester Town Hall. She earlier announced that her verdict is expected around "breakfast time" this morning local time, triggering speculation over whether it would be an early breakfast or a late one – based on how the counting trends pan out.
Brisk voting marked polling day yesterday as the results remained too close to call till the very last minute. Experts predicted a high turnout would benefit the Remain campaign.
The final announcement will bring to a close a fever-pitched and highly-strung campaign by both the Brexit and Remain sides. There has been
much speculation about how the final outcome would impact David Cameron's own political future as Prime Minister.
While he has repeatedly stressed that the 2015 General Election has given him the mandate to continue irrespective of the result, the bitter campaign had exposed a deep divide within his own Conservative party.
However, more than 80 Eurosceptic MPs from his party, including leading Vote Leave campaigner Boris Johnson and Indian-origin minister Priti Patel, moved quickly to calm the internal turmoil by urging Cameron to stay on as PM in a letter delivered to him soon after the polls closed last night.
"We who are supporters of Vote Leave and members of the Conservative Party thank you for giving the British people a choice of their destiny on 23 June. We believe that whatever the British people decide you have both a mandate and a duty to continue leading the nation implementing our 2015 manifesto," the letter states.
Both sides of the campaign had urged the over 46 million registered voters, including 1.2 million British Indians, to brave rains and flooding to cast their votes.
In some areas, booths had to be shut and moved to a different location due to water-logging but the general spirit remained on a high throughout the day.
Cameron voted early near Downing Street after he had closed the campaign with the message to voters to "get out there and vote Remain" and reject the "untruths" of the camp in favour of Brexit or Britain' s exit.
On the opposing side, former London mayor Boris Johnson, heading the final drive for the Vote Leave campaign, had hoped Friday could mark the UK's "independence day".
While the Remain camp, led by Cameron, had campaigned for economic certainty and safety of jobs, the Brexit camp had made their case as a vote to take back control of the UK's borders and finances. Immigration had been the central theme throughout and expected to swing most of the votes in favour of Brexit.
Indian-origin voters, the biggest ethnic minority group in the UK of an estimated 1.2 million, had reflected a divided house in line with the country-wide knife-edge divide in the four-month-long referendum campaign.
A British Election Study (BES) had found that 51.7 per cent of them were against Brexit, compared to 27.74 per cent in favour of leaving the economic bloc.
However, a significant percentage (16.85 per cent) of those who fell into the "Don't Know" category in the study last month were expected to hold the key to the results.
The referendum ballot paper asked the question: "Should the United Kingdom remain a member of the European Union or leave the European Union?" Voters have the option to mark a cross next to either "Should remain in the EU" or "Should Leave the EU," with the winning side needing more than half of all votes cast.
In a departure from the norm, no major broadcasters had commissioned any exit polls over concerns about accuracy.
The bookmakers, however, had seemed more confident about a Remain vote, and saw a flurry of late activity as the referendum became the biggest political betting event in history with an estimated 100 million pounds being wagered.
Numerous hedge funds had commissioned their own exclusive exit polls at a cost of up to 500,000 pounds, which asked people how they voted on their way out of polling stations.
The results were intended to help traders get an insight into the way the vote would go ahead of the public, with these polls remaining private.