British Prime Minister Rishi Sunak has unexpectedly called an early election for July 4 as his Conservative Party seeks to defy dire opinion polls that show it trailing Labour.

A wet Sunak, 44, made the announcement in the driving rain outside his Downing Street office, ending months of speculation as to when he would call a new vote.

An election did not legally have to be held until January 2025.

Sunak visited the King to inform the monarch of the rare summer election. Buckingham Palace said the royal family would postpone engagements that “may appear to divert attention or distract from the election campaign”.

The PM’s surprise move is a risky strategy given the Conservatives, who have been in power for 14 years, are widely expected to lose to the Labour Party.

Sunak’s speech was almost drowned out by protesters playing the Labour Party’s 1997 theme tune under Tony Blair — ‘Things can only get better‘ by Northern Irish band D:Ream.

Nationwide TV coverage, including from the BBC, shows him having to shout to be heard over the blasting tune.

Sunak listed what he said were his achievements in government, not only as PM but also as a former finance minister.

“Now is the moment for Britain to choose its future,” he said, describing that choice as one between stability with him and the unknown with Labour leader Keir Starmer.

“Over the next few weeks, I will fight for every vote, I will earn your trust and I will prove to you that only a Conservative government led by me will not put our hard-earned economic stability at risk.”

In an attack on Labour, Sunak said that Starmer, conversely, always took the “easy way out” and had no plan.

“As a result, the future can only be uncertain with them,” he said.

Sunak heads into the election not only far behind the Labour Party in the polls but also somewhat isolated from some of his fellow Tories, increasingly dependent on a small team of advisers to steer him through the campaign.

But he seems to have decided with some economic gains, such as inflation falling and Britain’s economy growing at its fastest pace in almost three years, now was the time to take a risk and present his agenda for a new term formally to voters.

The former investment banker and finance minister took office less than two years ago. Since then has struggled to define what he stands for, becoming increasingly frustrated that what he sees as his successes have failed to be appreciated.

Both parties have all but kicked off campaigning for an election, with the attack lines on the economy and on defence already firmly drawn.

Sunak and his government accuse Labour of being poised to increase taxes if in government and that the party would not be a safe pair of hands for Britain in an increasingly dangerous world as it lacks a plan, charges the opposition denies.

Labour accuses the government of 14 years of economic mismanagement, leaving people worse off, with a series of chaotic administrations that have failed to give the stability businesses have craved to spur economic growth.

If Labour wins the election, Britain, once known for its political stability, will have had six prime ministers in eight years for the first time since the 1830s.

Starmer said his party would return Britain to the “service of working people”.

“The future of the country is in your hands,” he said. “Together we can stop the chaos, turn the page and start to rebuild Britain and change our country.”

Before the announcement, Labour said it was more than ready for an election.

“We are fully ready to go whenever the Prime Minister calls an election. We have a fully organised and operational campaign ready to go and we think the country is crying out for a general election,” Labour leader Starmer’s spokesperson said.

Starmer kicked off Labour’s election campaign last week by pledging to “rebuild Britain”, setting out the first steps he said it would take if it formed the next government.

Labour Party leader Sir Keir Starmer arrives at Westminster after the election was called. Photo: Getty

Labour is about 20 percentage points ahead of Sunak’s Conservatives in the opinion polls but some party officials are concerned its advantage is not as solid as it appears, fearing many voters remain undecided.

Sunak might be aiming to capitalise on that uncertainty and also to wrongfoot Labour, which has still to complete the selection of all its parliamentary candidates, a party veteran said.

Sunak will also hope that some economic gains and the first flights in his centrepiece immigration plan of sending illegal asylum seekers to Rwanda might also boost his party’s fortunes.

The earliest possible date for those flights is June 24, 10 days before the election.

-with AAP