More than half of voters want Keir Starmer to resign as Prime Minister - and his would-be replacement Andy Burnham is already declining in popularity, according to a new poll.

An Opinium survey found 55 per cent of respondents believe Sir Keir should quit as Labour leader and leave Downing Street.

This compared with just one quarter (25 per cent) who think he should remain in post and continue to lead the country.

The research also found that Mr Burnham is the only potential Labour successor to Sir Keir who is viewed more positively than negatively by the public.

He recorded a net acceptability score of +8, ahead of John Healey (-8), Al Carns (-10) and Wes Streeting (-16).

But Mr Burnham's standing has fallen by 12 points since May, representing the largest decline among Sir Keir's possible replacements.

It comes amid feverish speculation that Sir Keir will announce as early as Monday that he is quitting in the wake of Mr Burnham's thumping win in the Makerfield by-election.

The PM is said to have reached the conclusion that his position is no longer tenable after talking to Cabinet colleagues, No 10 advisers, union leaders and key Labour donors.

But Downing Street responded by insisting the position was unchanged from Friday when the PM vowed to fight on and said that he would contest any leadership challenge.

Sir Keir, as the incumbent Labour leader, will automatically be on the ballot in a leadership contest - should he choose to be - if Mr Burnham or another challenger gathers the required support of 81 Labour MPs needed to trigger a contest.

The Opinium poll found 44 per cent of the public think Sir Keir should not run in a leadership contest, compared to 35 per cent who think he should seek re-election as Labour leader.

When voters are asked directly who they would prefer as PM, Mr Burnham leads Starmer by seven points (26 per cent to 19 per cent).

Mr Burnham also comfortably outperforms Mr Streeting, the former health secretary, in a head-to-head comparison.

Sir Keir's approval rating was unchanged in the latest survey at net -42, with Tory leader Kemi Badenoch outperforming other major party leaders on net -4.

Reform UK's Nigel Farage has slipped slightly to -21, while Green leader Zack Polanski has improved to -16.

When asked who would be the best PM, voters narrowly chose Mrs Badenoch over Sir Keir by 23 per cent to 22 per cent, while Mr Farage also maintains a narrow lead over Sir Keir (27 per cent to 26 per cent).

In both cases, around four in ten respondents choose neither option.

When voters were asked who they would support at a general election, Reform continued to lead on 27 per cent despite a two percentage point fall since earlier this month.

Labour remained on 20 per cent, while the Conservatives edged up to 18 per cent. The Greens stand on 14 per cent and the Liberal Democrats on 12 per cent.

Opinium's James Crouch said: 'Andy Burnham's victory in Makerfield has transformed the political narrative and given him the chance to ride a wave of Keir Starmer's unpopularity.

'However, our polling suggests before the Makerfield result was announced that Labour voters still wanted Starmer to contest any leadership race and had little appetite for an immediate leadership election.'

Opinium surveyed 2,050 UK adults between 17 to 19 June, with the majority of fieldwork done before the result of the Makerfield by-election was known.