LONDON: In a historic development, the UK has voted to leave the European Union after 43 years as the 'Brexit' camp today took a seemingly unassailable lead over the 'Remain' camp in a down-to-wire referendum with far reaching implications for the world.

52 per cent of the Britons in Thursday's vote favoured leaving the 28-member EU, while 48 per cent supported staying in the bloc, according to a BBC forecast after counting of 70 per cent of votes.

The national broadcaster said that the trends indicated that the Remain side spearheaded by Prime Minister David Cameron 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.

The final national result is to be officially declared by the UK Electoral Commission's chief counting officer Jenny Watson from Manchester Town Hall.

"... Dawn is breaking on an independent United Kingdom June 23 will be our Independence Day," far-right UK Independence Party (UKIP) leader Nigel Farage said, while declaring victory.

London and Scotland voted strongly to stay in the EU but the remain vote has been undermined by poor results in the north of England, it said. Voters in Wales and the English shires have backed Brexit in large numbers.

As expected the, the result sent ripples across the world as the pound fell to its lowest level against the dollar since 1985. Japan's benchmark Nikkei was down 7.7 per cent to 14,982.48 points.

In South Korea, the Kospi index was 3.9 per cent lower at 1,909.18. In China, the mainland Shanghai Composite was down 1.2 per cent to 2,857.58 while Hong Kong's Hang Seng is down sharply 4.7 per cent to 19,894.12 points.

The vote - which saw an extremely high turnout of around 72 per cent with over 30 million people voting- 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 UK will be the first country to leave the bloc.

The argument has swiftly moved to the future and what happens next after the Brexit vote.

While the result of a referendum is not legally binding on the UK government, 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.