London - Prime Minister Boris Johnson’s Conservative party lost control of key councils in London, according to partial results from local and regional UK elections on Friday, with a potentially historic change looming in Northern Ireland.

The main UK opposition Labour party of Keir Starmer won in Tory “crown jewels” in the capital, including Margaret Thatcher’s “favourite” council Wandsworth, and Westminster for the first time since it was created in 1964.

Around two-thirds of votes for councils in England have been counted. Full results for Scotland, Wales and Northern Ireland are due on Friday evening and over the weekend.

The contest for the devolved assembly in Belfast could see a pro-Irish nationalist party win for the first time, with huge constitutional implications for the four-nation UK.

Predicted victors Sinn Fein -- the former political wing of paramilitary group the IRA -- are committed to a vote on reunification with the Irish republic to the south, a century after the island was partitioned.

The English results so far are not a landslide for Labour, which is seeking to capitalise on a cost-of-living crisis and Johnson’s own performance, including his unprecedented police fine for attending a lockdown-breaking party at Downing Street.

Johnson called the results “mixed” and said he took responsibility. “We had a tough night in some parts of the country but on the other hand in other parts of the country you are still seeing Conservatives going forward,” Johnson told reporters in his constituency on the outskirts of London.

But Starmer, visiting Barnet in northwest London, where Labour seized control of the council from the Tories, hailed what he called “a big turning point”.

“When it comes to London, you can hardly believe those names come off our lips. Wandsworth! They’ve been saying for years ‘You’ll never take Wandsworth from us.’ We’ve just done it! Westminster! It’s an astonishing result,” he told supporters.

‘Catastrophic’

The Conservatives are hoping to extend their 12 years in power for another term at the next general election, which is due by 2024. Johnson, 57, won the last general election in 2019 by a landslide on a promise to take the UK out of the European Union, and reverse rampant regional inequality.

Despite making good on his Brexit pledge, the coronavirus pandemic largely stalled his domestic plans. But his position has been put in jeopardy because of anger at lockdown-breaking parties at his Downing Street office and the steeply rising cost of living.

Poor results could reignite questions about his leadership, putting his position in jeopardy.

Police on Friday said they were launching a formal probe into claims that Starmer had also breached Covid rules with a campaign gathering in 2021, slightly taking the heat off the Conservatives.

Labour is bidding to leapfrog the Conservatives into second place in Scotland, behind the pro-independence Scottish National Party (SNP), and remain the largest party in Wales, where 16- and 17-year-olds are eligible to vote for the first time.

Sinn Fein rise

Numerous polls have predicted that Sinn Fein will be the biggest party in the contest for the 90 seats at the Northern Ireland Assembly, ahead of the pro-UK Democratic Unionists (DUP) and cross-community Alliance.

Sinn Fein leader Michelle O’Neill and her DUP and Alliance counterparts Jeffrey Donaldson and Naomi Long were all returned to their seats, with counting expected to stretch into late Friday or even resume on Saturday.

Early indications were that turnout was about 54 percent -- down from nearly 65 percent in 2017.

Sinn Fein has dialled down its calls for Irish unity during campaigning, saying it is “not fixated” on a date for a sovereignty poll, instead focusing on the rising cost of living and other local issues. O’Neill told reporters the election was “about the future”, promising a collaborative approach. But she played down a threatened DUP boycott if she becomes first minister that would collapse the assembly and trigger potentially lengthy talks to revive power-sharing.

“I will turn up on day one,” she vowed.

The DUP withdrew its first minister Paul Givan in February in protest at post-Brexit trade arrangements that the party says threatens Northern Ireland’s wide place in the UK.