Polls have closed across England, Scotland and Wales and votes will be counted over the coming days in the largest test of political opinion outside a general election.
On what has been dubbed Super Thursday, voters took part in contests which could shake up British politics and have profound implications for the future of the United Kingdom.
Labour faces a humiliating loss in Hartlepool in a blow to Sir Keir Starmer’s leadership.
Votes are being counted in the by-election with Labour fearing Boris Johnson will demolish another brick in the “red wall” of the party’s former northern heartlands.
The Hartlepool parliamentary contest is the main focus and it looks set to show how hard Sir Keir’s job of rebuilding support for Labour will be.
Tories at the by-election count were confident of victory, while early results in council contests in the north-east also appeared to show voters deserting Labour.
Bookmakers have made Tory Jill Mortimer favourite to take the seat in a rare by-election victory for a governing party, with a result expected early on Friday.
Shadow transport secretary Jim McMahon earlier conceded Labour has not “got over the line” in Hartlepool.
Asked whether Labour would be claiming victory in the by-election, Mr McMahon told Sky News: “It would be difficult to do that given how we see the numbers beginning to pan out.”
Pressed on whether he was conceding defeat, he added: “It is pretty clear in the way the ballots are landing that we are not close to winning this despite our best endeavours, despite the hard work of many fantastic volunteers and despite a fantastic candidate, who of course is a local GP working at Hartlepool hospital who has been working on the frontline during the pandemic.
“And so I think we have given it our all but sometimes you don’t get over the line on the day.
“That’s where we are, that’s the reality of where we are. We haven’t got over the line, that’s quite clear from the ballots.”
Over the coming days results elsewhere could have an even more dramatic influence on the state of the nation’s politics.
Scottish National Party leader Nicola Sturgeon’s push for a second independence referendum means the stakes are high in the Holyrood contest, with results expected to be announced on Friday and Saturday.
The SNP is expected to emerge again as the largest party in the Scottish Parliament after the election, but it wants to win an overall majority of MSPs as it pushes for a second independence referendum – something which polls suggest remains in the balance.
Mr Johnson has refused to countenance another referendum, setting up the potential for constitutional fireworks over the coming years if Ms Sturgeon gets the outcome she desires.
The SNP leader insisted her focus would be on tackling coronavirus and rebuilding the economy.
But “when the Covid crisis has passed, we will give the people of Scotland the opportunity to decide if they want the recovery to be in the hands of the likes of Boris Johnson and the austerity-driven Tories or to put Scotland’s future in Scotland’s hands with independence”.
Results of the elections – which also include the Welsh Parliament, police and crime commissioners and English local authorities and mayors – are expected to continue filtering through until Monday as counting will take longer than normal due to coronavirus restrictions.
The Hartlepool contest will be one of the earliest results, with counting taking place overnight.
The seat was held by Labour with a majority of 3,595 in 2019, even as other bricks in the red wall crumbled – in part due to the Brexit Party splitting the Tory vote.
Both Mr Johnson and Sir Keir made three visits during the campaign in a sign of the importance it represents to their parties.
The Prime Minister insisted it would be a “very tough fight” to win Hartlepool, a seat that has been Labour since its creation in 1974.
But the Conservatives hope to achieve a “hat trick” of successes, winning Hartlepool and retaining the mayoralties in Teesside and the West Midlands.
Mr Johnson said: “It’s Conservative mayors who are bringing new investment and local jobs to their areas. A new freeport and green jobs are on their way to Teesside and new trams, Metro lines and station upgrades to the West Midlands.
“More has been delivered by Conservatives in four years than complacent Labour politicians have delivered in decades.”
If Hartlepool goes to the Tories it could be a difficult long weekend for Labour.
YouGov local election polling suggested the Tories could take over as the largest party in Bolton and Dudley, while Labour sources also fear they could lose control of both Sunderland and Durham councils for the first time in half a century.
Sir Keir said it would take time to rebuild his party after the worst general election result since 1935 under Jeremy Corbyn, adding: “I never thought we would climb the mountain we have to climb in just one year.”
In his final message to voters he sought to underline the shift from Mr Corbyn, stressing “this is a changed Labour Party” which was “under new leadership”.
But a senior Labour source admitted “it’s been a tough one” while shadow cabinet minister Thangam Debbonaire admitted the party’s message had not been cutting through.
Asked on the BBC’s Question Time if it would be “curtains for Keir” if Labour loses Hartlepool, she said: “I know that Keir has a vision for making this country the best country to grow up in, the best country to grow old in. I know we want to rebuild the economy. I know we want to build a better country to grow up and grow old in.
“We’ve got a great team who cannot wait to be able to cut through more and I hear what people are saying, it’s not cutting through, I get that.
“I think that’s a lesson for the Labour Party that we’re going to have to take into account.”
For Labour, success is expected in the form of Sadiq Khan winning a second term in London, probably late on Saturday.
In Wales, Mark Drakeford hopes to maintain Labour’s grip on the Senedd – but he may find himself forced to forge a new coalition to stay as First Minister.
That could mean talks with Plaid Cymru, whose leader, Adam Price, has committed to an independence referendum within five years if his party wins a majority.