Hartlepool once nearly triggered Keir Starmer’s resignation; local election results overnight mean it may yet do so in the coming days.

Five years ago, Labour crashed to a humiliating defeat in a byelection for the city’s Westminster seat, prompting Starmer to consider resigning as opposition leader.

On Thursday night, the party lost every single council seat it was contesting in the town to Reform UK, putting Starmer’s leadership in question once more.

The local Labour MP, Jonathan Brash, told the Guardian on Thursday night: “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.”

In Downing Street, where extra advisers have reportedly been brought in to help the prime minister survive the next few days, officials will be watching carefully to see if others follow Brash’s lead.

On Friday morning, most senior Labour MPs were keeping their powder dry after David Lammy, the deputy prime minister, urged colleagues to remain loyal. “You don’t change the pilot during a flight,” he said on Thursday night. “You carry on and you recognise too that governments sometimes, particularly incumbent governments, have it hard, but of course we will reflect on what we’re hearing from the electorate. There’s a lot of frustration.”

Starmer and his allies have long known that the local and devolved election results would be a perilous moment for the prime minister.

Robert Hayward, the Conservative peer and polling expert, had predicted the party could lose approximately 1,850 councillors in England, and polls suggested it will lose the Senedd in Wales and fall further behind the Scottish National party at Holyrood.

Early results from Thursday night showed Reform making significant ground, picking up council seats across the north and the Midlands, in former Labour heartlands such as Wigan, Bolton and Salford. Labour lost control of councils in Hartlepool, Tameside, Redditch and Tamworth.

By early Friday morning, Labour had lost more than 229 council seats – more than half of those it was contesting. Reform had gained 305 seats, making it the biggest winner from overnight counting.

One bright spot for Labour came from London, where the party proved more resilient than some were expecting, holding on to Hammersmith and Fulham council and defeating a strong Liberal Democrat challenge in Merton.

Hayward said: “The early results are as bad for Labour as predicted. They are probably slightly worse outside London, but slightly better inside the capital, which looks like it will be different from the rest of the country.”

John Curtice, the polling expert and professor of politics at the University of Strathclyde, said the night was proving to be one of “substantial success” for Reform.

The Conservatives also suffered heavy losses to Nigel Farage’s party, losing 122 council seats in England. However, the Tories celebrated success in Westminster, where it regained control of the council from Labour.

The Liberal Democrats said they were expecting an eighth set of local election gains in a row, while the Greens were hoping to make headway with results later in the day.

As Starmer contemplates one of the party’s worst set of election results in history, he may take solace in the fact that every one of his likely challengers is facing heavy losses in their own patch.

Labour lost control in Tameside, for example, which is the former deputy prime minister Angela Rayner’s local council. And it struggled in other places across the north-west, where the Greater Manchester mayor, Andy Burnham, is hoping to find a Westminster seat in the coming months.

Experts also expect the party to do badly in Redbridge, the council that is home to Wes Streeting, the health secretary.

Hayward said: “The one bright spot so far for Starmer is that all his natural challengers are seeing their own base swept away.”