The polls have closed across Britain in the biggest set of votes since the 2019 general election.
Throughout Thursday, voters picked representatives for the Scottish Parliament and Welsh Senedd as well as mayors and local councils in England.
Voters in England and Wales also voted for police and crime commissioners.
The results are due to come in over the next few days – with the outcome of the Hartlepool by-election expected on Friday morning.
But Labour’s shadow transport secretary, Jim McMahon, has already admitted defeat over the Westminster seat, telling the BBC his party “hasn’t got over the line”.
Due to the coronavirus pandemic, elections in 2020 were postponed – leading to a particularly large set of polls taking place this year.
The elections are Sir Keir Starmer’s first major political test since becoming Labour leader a year ago.
The results will give an indication of whether the party is recovering from its heavy defeat in the 2019 general elections.
Conservatives hope to build on their success in the general election, when they were able to flip several constituencies previously considered Labour strongholds.
Both parties will be closely watching the result of the by-election in Hartlepool – a seat currently held by Labour.
But the BBC’s political editor in the North East, Richard Moss, said it appeared that the party’s majority of 3,595 has been “whittled away” by the Tories in Thursday’s poll and they could be on course for a “significant win”.
Labour’s Mr McMahon told the BBC: “It’s quite clear when we see the ballots landing on the table that we just haven’t got over the line on the day… that’s clearly very disappointing.”
In Scotland, the results will give an indication of the public level of support for a second independence referendum, as proposed by the SNP.
Meanwhile, the Welsh Labour party are aiming to remain the largest party in the Senedd, where they have held power since the parliament was founded in 1999.