Britain voted on Thursday in a deeply divisive election that posed a historic choice between an imminent split from the European Union and another referendum that could scrap the entire Brexit process.

A decisive victory for Prime Minister Boris Johnson in the third poll in less than five years would almost certainly end Britain's 46-year involvement in the European project at the end of next month.

The kingdom would cut ties with its closest trading partners and look to regain the legal and border controls Brexit supporters sought in the original 2016 EU membership vote.

But a win for the opposition, or a hung parliament, could still reverse Brexit and give Britain a hard-left government headed by Labour party leader Jeremy Corbyn - a veteran socialist committed to renationalisation and massive public sector spending.

Britons braved winter storms and howling winds as they lined up to cast ballots in what Johnson and Corbyn have both called the most important vote in a generation.

Johnson voted in London with his dog Dilyn - a furry Jack Russell he picked up and kissed before a swarm of reporters - while Corbyn was greeted at his polling station by a protester dressed up as the "Sesame Street" character Elmo.

Opinion polls show Johnson's ruling Conservatives heading for a narrow majority.

But the pollsters were almost unanimously wrong about the last general election in 2017 and Johnson has said the outcome rested on a "knife edge".

The British pound was down nearly one percent against the dollar in expectation of exit polls at 2200 GMT. The first official results are due to start coming in an hour later.