In London, Labour's Sadiq Khan defeated Conservative Zac Goldsmith to become mayor. Khan came out on top in three constituencies that had voted for former mayor of London Boris Johnston in 2012. As Khan does not have 50% of first preference votes, second preferences are being counted.
The Labour candidate gained 44.2% of first preference votes, with Goldsmith securing 35%. Green Party candidate Sian Berry came in third with 5.8%.
The mayor has control over four major policy areas in London - transport, policing, environment, and housing and planning - and the London Assembly scrutinises the mayor's policies.
Of the 14 London Assembly seats, Labour won nine, taking Merton and Wandsworth from the Conservatives, who held five boroughs.
What happened in Scotland?
The SNP will retain its grip on government, after having claimed 59 of the 73 constituency seats up for grabs - up six on their 2011 result. Overall, the SNP will occupy 63 of the 129 seats at Holyrood, with the Conservatives becoming the second-largest party on 31. Labour took 24, the Greens six, and the Lib Dems five.
Some of the SNP's gains came at Labour's expense in Glasgow, which now represents a clean sweep for the governing party. It also took Edinburgh Northern and Leith from Labour.
But it faltered elsewhere in the capital, losing Edinburgh Central to the Conservatives and Edinburgh Western to the Lib Dems. The Scottish Labour Party recaptured Edinburgh Southern from the SNP.
The Labour party's share of the constituency vote in Scotland was concentrated in areas where it largely failed to get over the finish line ahead of the SNP.
The SNP, on the other hand, dominated the count nearly everywhere in the country, winning more than 30% of the vote in all but three constituencies.
The Scottish Conservatives increased their share of the vote by more than eight percentage points, once again doing best along the border with England, but their strong performance in Aberdeenshire and Perthshire was enough to win them one constituency seat there too. With regional results factored in, the party gained 16 seats on the previous election in 2011 and will now be the second-largest party in the Scottish parliament.
That the Lib Dems doubled their constituency seat count, from two to four, masks a dismal night for the party, which lost its deposit in 48 constituencies.
In Wales...
Labour is likely to hang on to power in Wales, with just one constituency changing hands, as Plaid Cymru leader Leanne Wood captured the Rhondda from the governing party.
The biggest shift in Welsh politics overnight is the rise of UKIP, which has won seven regional seats.
Although UKIP did not manage to clinch any constituency seats, they did have five places where they won more than 20% of the constituency vote: Merthyr Tydfil and Rhymney, Newport East, Islwyn, and Torfaen, where it came in second place, and Caerphilly, where it came third.
In three of these seats, UKIP's gains appear to have come mostly at Labour's expense, in one the losses were shared fairly evenly between Labour and the Lib Dems, and in one the Lib Dems lost out the most. The Conservatives also lost vote share in three of the five constituencies, but to a lesser extent.
