Labour lost almost 1,500 councillors in local elections across England amid a surge for Nigel Farage’s Reform UK, with the Greens also eating into the party’s support in London and other urban areas.
It was also kicked out of power in Wales, where it has enjoyed political dominance for a century, and returned just 17 of the 129 seats in the Scottish Parliament, its worst ever result at a Holyrood election.
Sir Keir now faces another key hurdle on Monday, when backbench MP Catherine West says she will seek to trigger a leadership contest against him if she is “still dissatisfied” after his reset speech.
West, a former junior minister, is not bidding to be the next Labour leader herself, but by triggering a leadership she could flush out heavyweight contenders she thinks could do a better job than Sir Keir.
More than 30 Labour MPs have publicly called for the prime minister to resign or to set out a timetable for his departure.
However, Burnham cannot enter a contest without first becoming an MP, under the party’s rules for leadership contests. The mayor’s supporters are hoping a leadership contest can be delayed until he is able to return to Parliament.
Rayner resigned as Sir Keir’s deputy prime minister last September after it emerged she had failed to pay the correct amount of stamp duty on a £800,000 flat in Hove.
It has been widely reported that she is still waiting for the result of an HMRC investigation into the purchase, which could complicate any immediate leadership campaign.