British Prime Minister Theresa May has called an early election on June 8 in a bid to strengthen her hand in the UK’s negotiations to leave the European Union.

Ms May announced the surprise move Tuesday night, breaking her often-repeated vow not to call an election before its scheduled 2020 date.

The Prime Minister emphasised the need for unity in the UK Parliament, saying an election was the only way to guarantee political stability for the years ahead in its negotiates with the EU.

The pound strengthened by almost half a cent against the US dollar as Ms May made the announcment, reflecting investor relief that earlier rumours of a shock resignation did not transpire.

“I have just chaired a meeting of the cabinet where we agreed that the government should call a general election to be held on the 8th of June,” Ms May said in a surprise statement outside her Downing Street office on Tuesday.

“It was with reluctance that I decided the country needs this election, but it is with strong conviction that I say it is necessary to secure the strong and stable leadership the country needs to see us through Brexit and beyond.”

She said she would introduce legislation on Wednesday to pave the way for the early election.

EU officials echoed Theresa May’s hopes that a fresh parliamentary election could strengthen her hand in managing the Brexit negotiations which are due to start around the same time.

“We have some hope that this will lead to a strong leader in London that can negotiate with us with strong backing by the electorate,” an EU official told Reuters.

EU negotiators have been concerned that division over Brexit among voters – and within May’s own party – could make it harder to agree terms before March 2019 to ensure an orderly British withdrawal.

Ms May’s Conservatives, who were split on the issue of EU membership ahead of last year’s referendum, are currently far ahead of Labour, the main opposition party, according to opinion polls.

Ms May said this was a one-off chance to get an election done while the EU was agreeing on its negotiating position.

She said the government had the right plan to negotiate Brexit, and there would be no change of course.

“Our opponents believe because the government’s majority is so small that our resolve will weaken and that they can force us to change. They are wrong,” she said.

Labour leader Jeremy Corbyn said he welcomed the prime minister’s decision. Photo: AAP

“They underestimate our determination to get the job done and I am not prepared to let them endanger the security of millions of working people across the country, because what they are doing jeopardises the work we must do to prepare for Brexit at home and it weakens the government’s negotiating position in Europe.”

In order to call the early election, Ms May will need the support of two-thirds of the 650 MPs in the Commons – but Labour is expected to support her, as any opposition would look weak if it did not agree to the chance to take office.

Senior Tories have urged Ms May to call an early election, taking advantage of the Conservatives’ healthy opinion poll lead over Jeremy Corbyn’s Labour.

Mr Corbyn said he welcomed the election announcement.

“I welcome the Prime Minister’s decision to give the British people the chance to vote for a government that will put the interests of the majority first.”

The Liberal Democrats said the snap poll was Britain’s chance to avoid a “disastrous hard Brexit” .

Party leader Tim Farron told voters “this is your chance to change the direction of your country”.

The Lib Dems have consistently called for a second referendum on the final Brexit deal May achieves after negotiations with the European Union, and want to keep the UK in the European single market.

-With agencies