UPDATE: As Britain awakes to the inevitable result of a hung parliament, Prime Minister Theresa May has left her Conservative party headquarters and arrived at 10 Downing Street in a “sobre, calm” mood.

The BBC is now reporting “no party can win a majority”.

With just nine seats left to declare, Thursday’s polls showed gains for the opposition Labour Party, the BBC reported, saying it was “seen as a humiliation” for Ms May who had called an early election.

By 3.45pm on Friday (AEST), the Conservatives had won 311 seats, Labour 260 seats, the Scottish National Party 35 seats and the Liberal Democrats 12 seats.

Earlier, Ms May held onto her seat of Maidenhead in the British general election despite earlier calls for her to resign and make way for a new government.

Ms May attracted 37,718 votes to her Labour counterpart’s 11,261 votes cast, addressing her supporters saying the UK now “needs a period of stability”.

The BBC was forecasting the Conservatives would end up with 322 votes, down from 330 before the election and short of a majority in the 650-seat House of Commons.

Speaking after being re-elected with 40,086 votes cast in his Islington North London seat, British Labour Party leader Jeremy Corbyn said Ms May should “go and make way for a government that is truly representative of this country.”

ABC analyst Antony Green, who is in the UK to cover the election, tweeted just after midday that 356 seats had been counted with the conservatives attracting 43.1 per cent of the vote share and Labor 39.7 per cent.

“Jeremy Corbyn has gained seats for Labour. He’s not going to be the next Prime Minister,” Mr Green earlier told ABC TV.

Prospects of a hung parliament

The UK now faces the prospect of a hung parliament after exit polls indicate a major loss of seats for Theresa May’s Conservative Party.

The traditionally accurate exit polls show the Conservatives holding 314 of the required 326 seats, with Jeremy Corbyn’s Labour Party holding 266.

The projected loss for the Conservatives is 17 seats, with a gain of 34 seats for Labour.

The political deadlock could derail negotiations with the other 27 European Union countries ahead of Britain’s exit from the bloc – due in March 2019 – before they even begin in earnest.

A delay in forming a government could push back the start of Brexit talks, currently scheduled for June 19, and reduce the time available for what are expected to be the most complex negotiations in post-World War Two European history.

What leaders are saying

As reports emerge Ms May may lose her parliamentary majority, Labour leader Jeremy Corbyn said: “Whatever the final result, our positive campaign has changed politics for the better”.

“If the result of this tonight is that we finish up without a government with a clear majority pushing for Brexit, then a huge gap opens in the political landscape for Ukip once again,” said former Ukip leader Nigel Farage.

British newspaper The Times said: “Theresa May hoped to transform the political map of Britain last night. Instead, early indications were that she has been humiliated and her party left without a working majority. She has gambled and lost.”

Exit polls

Based on interviews with 30,450 voters leaving polling stations across the country, the exit poll is conducted for a consortium of UK broadcasters and regarded as a reliable, though not exact, indicator of the likely result.

It projects 34 seats for the Scottish National Party and 14 for the Liberal Democrats.

If confirmed, the result will be a disaster for Ms May, who called a snap election in the hope of increasing her majority.

Mr Corbyn could attempt to form a government with the smaller parties, which strongly oppose most of Ms May’s policies on domestic issues such as public spending cuts.

Ms May’s failure to win a majority also calls her leadership into question and raises the possibility of a second election in Britain this year.

The first of the 650 seats are are expected to be called by 9am, with a final result by Friday afternoon or evening.

Former British finance minister George Osborne said if the exit poll forecasting proves to be correct, it would be “completely catastrophic” for Ms May and the Conservative Party.

“It is early days. It’s a poll. If the poll is anything like accurate this is completely catastrophic for the Conservatives and for Theresa May,” Mr Osborne told broadcaster ITV.

“It’s difficult to see, if these numbers were right, how they would put together the coalition to remain in office. But equally it’s quite difficult looking at those numbers to see how Labour could put together a coalition so it’s on a real knife edge.”

Britons went to the polls amid tight security in a snap election predicted to give Prime Minister May a larger parliamentary majority.

Ms May called the snap June 8 election in April hoping to strengthen her hand in looming divorce talks with the European Union.

But as many as one in five voters were still undecided this week after a seven-week campaign overshadowed in the later stages by two terror attacks that killed 30 people in Manchester and London in less than two weeks.

Most polling stations had increased security, with armed police expected to reinforce regular officers at some locations.

While security issues generally favour conservative parties, experts say the recent Manchester and London Bridge have failed to benefit Ms May.

Dr Todd K Hartman of the University of Sheffield said cuts to security budgets under the Conservative government’s austerity programmes has cast the conservatives in a poor light when it comes to combatting terrorism.

– With agencies