Britain's Labour party on Friday urged beleaguered Prime Minister Rishi Sunak to call a general election after making huge gains in English polls that included a seat in parliament.

Labour, out of power since 2010 and trounced by Boris Johnson's Conservatives at the last general election in 2019, won a host of local council seats and mayoral contests as well as the Blackpool South parliamentary seat.

Labour leader Keir Starmer said the emphatic victories nationwide, which included winning a new mayoral post encompassing Sunak's own northern English constituency, sent the prime minister a clear message to hold a nationwide vote.

"Voters in Blackpool South have sent a direct message to Rishi Sunak: make way, let's have a general election," he said after visiting Blackpool to congratulate the new MP there, Chris Webb.

Sunak must order a general election to be held by January 28 next year at the latest.

He insisted voters will re-elect his Conservatives, as he sought solace in a Tory mayor winning a third term in Tees Valley, in northeast England, albeit with a vastly reduced majority.

"Come a general election, (voters) are going to stick with us too," Sunak said, as he celebrated the rare Conservative win, for Ben Houchen, on an otherwise dismal day of results.

Labour enjoys a lead of around 20 points over the Tories in polls.

The embattled prime minister, in charge since October 2022, had earlier conceded results were "disappointing" so far but noted many were still to be announced.

"I am focused completely on the job at hand: that's delivering for people across the country," he told reporters.

- Mayor battles -

Labour began Friday by winning the Blackpool South constituency with a 26-percent swing -- the third-largest margin from the Tories to Labour at a by-election since World War II.

By late afternoon, the party had gained more than 100 councillors and several new mayors -- in northeast England, Yorkshire and in the East Midlands -- after voting on Thursday.

The Conservatives were on track to lose around half the nearly 1,000 seats they were defending.

If replicated in a nationwide contest, the initial tallies suggested Labour would win 34 percent of the vote, with the Tories trailing by nine points, according to the BBC.

Speculation has been rife in Westminster that a bad showing may lead some restive Conservative lawmakers to try to replace Sunak, forcing the prime minister to possibly call an immediate general election.

He has previously said he is planning on doing so in the "second half of 2024.

The 43-year-old has failed to improve his party's dismal opinion poll ratings since succeeding Liz Truss in October 2022.

Senior Conservatives played down the significance of the defeat in Blackpool South, noting it had been triggered by a lobbying scandal that saw the area's former Conservative MP resign.

Houchen's win also provided some respite.

The outcome of another key mayoral contest in the West Midlands is also seen as crucial for Sunak.

That result, involving moderate Conservative incumbent Andy Street, is not expected until Saturday.

The outcome of the London mayoral election, where Labour's Sadiq Khan is expected to win a record third term, is also due then.

- Right-wing upstarts -

The Tories were defending hundreds of seats they secured in 2021, when they led Labour in nationwide polls before the implosion of Johnson's premiership and Truss's disastrous 49-day rule.

Starmer said Friday's results showed that his party, beset by ideological infighting and claims of anti-Semitism under hard-left former leader Jeremy Corbyn, was rejuvenated.

The Tories are under fire nationally on issues ranging from cost-of-living to transport and health.

Voters are also turned off by infighting that has resulted in five prime ministers since the 2016 Brexit vote.

"We are probably looking at certainly one of the worst, if not the worst, Conservative performances in local government elections for the last 40 years," polling expert John Curtice told BBC radio.

The Blackpool South defeat was the Tories' 11th by-election loss this parliament, the most by any government since the late 1960s. Sunak has been in charge during seven of them.

Worryingly for him, the Conservatives only beat the fringe Reform UK party into second place by 117 votes in Blackpool.

The party linked to arch-Eurosceptic Nigel Farage won 17 percent of the vote, its best-ever by-election performance, suggesting it could squeeze the right-wing vote at the general election.

Labour lost control of one local authority, and suffered some councillor losses to independents elsewhere, due to what analysts said was its stance on the Israel-Hamas war.