The scale of the electoral challenge facing Labour has been laid bare as the party haemorrhages councillors at the local elections and Reform makes significant gains.

Keir Starmer’s party went into Thursday’s local elections expected to lose up to 1,850 councillors, with senior figures describing the contest as “tough”.

Initial results overnight painted a bleak picture for the prime minister, with Labour losing councillors in its traditional northern heartlands.

Reform took control of its first council at around 6am, gaining overall control of Newcastle-under-Lyme from Labour. The party’s leader, Nigel Farage, described the early results as a “historic change in British politics” and said his party was “scoring stunning percentages in traditional old Labour areas”.

The political scientist Prof Sir John Curtice told the BBC that while Reform was clearly winning the most votes in early counts, it had “probably not” reached 30% of the vote, an indication of the fracturing of British politics.

Curtice said: “It may well be now that Labour lose rather less than the 1,500 seats that perhaps some people said was potentially the tipping point for attempts to unseat Keir Starmer.”

He said: “[Reform] are basically being trailed by four parties that are all of them just a little bit below 20% or so, somewhere between 15 and 20%, but are actually at the moment quite difficult to disentangle.”

He added that the Greens were struggling to convert votes into seats because they were getting “far too many creditable second and third places”.

Reform were the runaway winners in north-east England. They won every single one of the 12 seats up for grabs in Hartlepool. It means Labour, which had a slim majority and was defending six seats, is likely to become the opposition.

Because only a third of the council was being elected, Reform will not have an outright majority. The party will have to make deals with independents in order to take control.

Labour councillors and supporters were noticeably despondent at the count in Brierton sports centre. The town’s Labour MP Jonathan Brash watched his wife, Pamela Hargreaves, the leader of Hartlepool council, lose her seat.

He told the Guardian he was angry and repeated his call for Starmer to go.

“It has been a terrible night for the Labour party,” he said. “What I’ve seen here is extraordinarily good, hard-working Hartlepool people lose their seats. I’ve seen canvassers working night and day in this election and it’s all been for naught and the reason has absolutely nothing to do with them.

“They are delivering for this town, they have been delivering for this town and the reality is we need change at the top of the Labour party.

“I think the very best thing the prime minister could do now is address the nation tomorrow and set out a timetable for his departure. We can then have an orderly transition, one that, by the way, ensures the full breadth of talent within the Labour party is able to stand, should it want to.”

John McDonnell, the former shadow chancellor under Jeremy Corbyn, said a leadership change must be “on the agenda” if the results overall prove “the nightmare as we are worried it will be”. But he added: “If there is to be a leadership change, it has to be an orderly transition, not a coup.”

The Green deputy leader, Rachel Millward, told the BBC her party was optimistic about taking control of Hackney council in east London and said: “We will make some exciting breakthroughs ... this will be seen as a step change moment for us as a party.” But she suggested that because of the electoral system the number of seats gained would not match the Green share of the vote across the country.

The Liberal Democrat deputy leader, Daisy Cooper, hailed the party’s “stonking results” in local elections so far, pointing to the party taking control of councils in Stockport and Portsmouth. She said in a statement: “The Liberal Democrats are on a record-breaking winning streak. We are heading for our eighth set of local election gains in a row and are on track to beat Labour and the Conservatives once again.”

The turnout was 31.5%, slightly higher than the 28% of the last local elections in 2024.

In Halton, Cheshire, Labour held two of the 17 seats it was defending as Reform UK gained 15 councillors in the first council to complete its count on Friday. In some wards, Reform won with more than 50% of the vote in an area where last year it won the Runcorn and Helsby byelection by just six votes.

Although Labour’s starting position means it retains control of Halton council, the shift in vote share combined with losses elsewhere in the north-west point to a difficult night for Starmer.

Those results included losses to Reform in Chorley, Lancashire, and Wigan, Greater Manchester.

In Wigan, represented in parliament by Lisa Nandy, the culture secretary, Labour lost 20 seats and Reform gained 23, but the authority remains Labour-controlled.

Elsewhere, Redditch and Tamworth changed from Labour to no overall control, while the Liberal Democrats took control of Stockport.

In Oxford city council, Labour lost two seats to the Greens but was expected to continue to be the biggest party and maintain its minority administration after winning in 10 wards. The Greens gained three seats overall after winning nine wards.