Elections 2016: Super Thursday results at a glance
Labour loses out as SNP claims victory in Scotland, while Ukip wins its first seats in Welsh Assembly
Nicola Sturgeon has claimed victory for the Scottish National Party in the Holyrood election.
However, the real upheaval came in the battle for second place, with Labour pushed into third place after losing a series of constituencies to the Nationalists and the Conservatives.
Here's what we know so far:
With 63 seats, the SNP is the largest party in the Scottish Parliament and will form a minority government at Holyrood. Labour won 24 seats, a loss of 13, while the Scottish Tories took 31, picking up an extra 16 to make them the second-largest party north of the border. The Greens won six seats and the Liberal Democrats retained five.
"Labour lost a series of constituencies including the prized seat of Eastwood near Glasgow, which fell to the Conservatives after 17 years in Labour's hands," The Guardian reports.
However, it's not all good news for the Nats, who have lost two key seats, giving up Fife North East to Scottish Liberal Democrat leader Willie Rennie and the Edinburgh Central seat to Scottish Conservative leader Ruth Davidson.
Davidson hailed a "very good night" for her party, but said they still had to win the trust of voters. "I am under no illusion that everybody who voted for me in that seat is a true-blue, dyed-in-the-wool Tory and neither are they in places up and down Scotland," she said. "They are people who want us to do a very specific job and that it is to hold the SNP to account."
Labour's vote withered in the Welsh Assembly election, with results showing a 7.6 per cent swing against the party. This translated into a loss of just one seat, but meant the group fell short of a majority.
Plaid Cymru leader Leanne Wood won in Rhondda, making her party the second largest with 12 seats, while the Conservatives have 11 and the Liberal Democrats one.
Ukip won its first seats in the assembly, with former Tory MP Mark Reckless among seven members elected via the regional lists.
England's local elections saw Labour lose 24 seats, although the party has kept control of all but one of the councils it held, losing only in Dudley, where there is now no overall majority.
The Conservatives also lost 24 seats, although maintained its 30 councils. The Liberal Democrats gained 29 seats and one council, while Ukip gained 24 seats and the Greens lost four. The Respect party lost all of its five seats.
Counting is still underway for the new London mayor, the London Assembly, police and crime commissioners and the Northern Ireland Assembly.
Super Thursday: A guide to the big election battlegrounds
Voters across the UK head to the polls today for local, mayoral and devolved assembly and parliamentary elections. While turnout is expected to be as low as 40 per cent, the outcome will have a significant impact on Britain's political landscape.
More than 2,700 seats are up for grabs in 124 English local councils, while parliamentary by-elections will also be held in the Labour strongholds of Ogmore and Sheffield Brightside & Hillsborough.
The vote has been touted as the first electoral test of Labour leader Jeremy Corbyn, who says his party will not lose seats. However, even before the row over anti-Semitism broke out, polling guru Professor John Curtice said Labour was on course "to suffer its worst result in opposition for 34 years", predicting it could lose as many as 170 local councillors.
The London mayoral race
The battle to succeed Boris Johnson as London mayor has been described as one of the most vicious and personal since the position was created in 2000. It has become a straight fight between Conservative Zac Goldsmith and Labour's Sadiq Kahn, who has distanced himself from the party leadership. With last-minute polls putting Khan's lead as high as 12 percentage points, it appears the controversy over Corbyn has not affected his chances. A strong showing for Labour in London, in what is otherwise expected to be a dismal night for the party, could save the party leader's job.
There is likely to be less positive news for Labour north of the border, where they are locked in a fierce battle with the Scottish Conservatives for second place. If the polls are correct, the SNP is all but guaranteed to retain its majority in Holyrood, although some pollsters have raised doubts over whether the Nationalists will win as many seats as they did in 2011.
Welsh and Northern Ireland Assemblies
In Wales, Labour is in a fight to remain the largest party, with Plaid Cymru forecast to at least solidify its position as the second party and the Conservatives in third. In Northern Ireland, few are predicting that the DUP-Sinn Fein duopoly will be broken.
Police and crime commissioners
Forty police and crime commissioners (PCCs), who will lead most of the local police forces in England and Wales, will also be elected today.
These races receive very little coverage and have attracted extremely low turnout. As such, says The Independent, they are "dependent on highly volatile local factors".