Polling has opened across England, Scotland and Wales in a series of local, mayoral and parliamentary contests – the biggest electoral test Keir Starmer and the Labour government have faced since the 2024 general election.

As millions of people across Great Britain go to the polls on Thursday, party leaders are poised for a set of results that could fundamentally change the political landscape nationally in Scotland and Wales, and across local authorities in England.

The results will be closely watched by all parties, and are seen as the first major political test of an increasingly multiparty system. They come after months of Labour and the Conservatives languishing in the polls, and the growing popularity of smaller parties such as Reform UK, the Greens and the Liberal Democrats.

The elections cover the Scottish and Welsh parliaments and 136 local councils in England, where 5,014 seats are being contested, including every one on all of London’s 32 borough councils, more than a dozen borough councils, six unitary councils, six county councils and three district councils. A further 73 councils are holding elections for half or a third of the seats available.

There are also six mayoral contests – in Croydon, Hackney, Lewisham, Newham, Tower Hamlets and Watford.

The polls for local elections will be open between 7am and 10pm, with the first results expected at aabout 12.30am on Friday, and a glut of further results from about 3am onwards.

About a third of councils should have declared results by around 7am, while the most significant results – including the mayoral results in London boroughs, and council results in Manchester and Leeds – starting to come in at lunchtime.

By the end of Friday about 80 more councils will have declared results, but the final councils – including Croydon and Tower Hamlets in London and Hastings in Sussex – won’t declare until Saturday afternoon.

Results in Scotland and Wales should become clear by about 4pm on Friday, with more local election results announced in the late afternoon and early evening.

Counting for mayoral elections will only begin on Friday, with Hackney and Newham expected to declare at 1pm, Watford at 2pm, Lewisham at 3pm, Croydon at 4pm and Tomer Hamlets at 6pm.

After the May 2025 local elections, Labour held 34% of all council seats in England, down 2% from 2024. The Conservatives fell to 26%, down 4% from the previous year and the Liberal Democrats held 19%, up 1%. The number of councillors represented by other parties increased from 11% to 12%. The Greens held 5% of seats, a similar share to 2024. Reform went from zero to 5% with the election of 677 councillors.

In Scotland, 129 MSPs will be voted into Holyrood, where they will debate and pass laws on all devolved matters, including education, health and transport. Policy areas with a UK-wide or international impact, such as defence, foreign policy and immigration are decided in Westminster.

At the last Scottish parliament election in 2021 the SNP won 64 seats – one short of a majority – and the Scottish Conservatives came second with 31. Scottish Labour came third with 22 seats, the Scottish Greens took eight and the Scottish Liberal Democrats, four.

Polls will be open in Scotland from 7am until 10pm. Unlike in previous years, counting of votes will be on Friday morning, with the first declarations expected at lunchtime and most results declared by the evening.

Welsh voters will elect 96 representatives across 16 constituencies, with six members of the Senedd in each. Electoral changes mean that a new proportional voting system will be in place. Voters will be asked to back a party rather than a candidate, with six Senedd members voted in based largely on the proportion of votes they get in a constituency.