Keir Starmer suffered fresh woe today as a bombshell poll showed Labour is on course for huge losses in London at next month's local elections.
A YouGov model predicted the Green Party and Reform UK will make a major breakthrough at borough council contests on 7 May.
In a challenge to Labour's recent dominance in the capital, the Greens are projected to win the highest vote share on four London councils.
The research also predicted Reform will win the highest vote share in three boroughs.
The MRP (Multilevel Regression with Post-stratification) model, based on polling of thousands of voters, suggested Labour is on course for its worst result in London in 50 years.
Sir Keir's party is projected to win the highest vote share in 15 councils, which would be six lower than in 2022.
Allies of the embattled Prime Minister, who is under intense pressure over the Peter Mandelson scandal, are braced for a leadership challenge after May's elections.
As well as council contests in London and across England, elections are also being held for the Scottish Parliament and Welsh Senedd next month.
Keir Starmer has suffered fresh woe as a bombshell poll showed Labour is on course for huge losses in London at next month's local elections
Half of London's 32 borough councils are judged by YouGov to be either 'very close' or 'super close' ahead of next month's contests
Labour is projected to win the highest vote share in 15 councils, which would be six lower than in 2022
Labour is expected to suffer a dismal set of results in all three countries as voters express their views on the unpopular PM.
The YouGov MRP projected the Greens, who have surged in support under 'eco-populist' leader Zack Polanski, will win the highest vote share in Hackney, Lambeth, Lewisham and Waltham Forest.
All four authorities in London have been long-held by Labour.
The model also predicted Nigel Farage's Reform will be the best-supported party in Labour-run Barking and Dagenham, Conservative-run Bromley, and Havering, which is currently under no overall control.
The Tories are on course to win the highest vote share in five councils and the Liberal Democrats in four, according to the research.
Lewisham and Hackney have not been run by a party other Labour since the 1970s, Waltham Forest since the 1980s and Lambeth since the 2000s.
Half of London's 32 borough councils are judged by YouGov to be either 'very close' or 'super close' ahead of next month's contests.
In 2022, Labour won 21 councils in London, with the Tories winning five and the Lib Dems winning three.
Patrick English, YouGov's head of elections, said: 'This is broadly reflective of what we are seeing nationally - a great big fragmentation of the vote into all these different parties.
'They're all eating each other's pies and creating this situation where the largest party vote shares for each council could be 23 to 25 percent of the vote.
'Fragmentation means that winning post gets lower and lower, and slight changes in the voting intention numbers could dramatically change the picture.'
A separate poll also suggested Labour could be swept away by a 'sea of Green' in parts of London next month.
A survey by Ipsos UK found 49 per cent of voters in the capital are considering backing the Greens on 7 May.
It also showed 44 per cent of voters in the capital are thinking about voting for Labour, with 35 per cent mulling giving their support to the Lib Dems.
Meanwhile, 28 per cent are considering voting for independents, while 16 per cent could support Reform.
Keiran Pedley, director of politics at Ipsos UK, said: 'Our data shows that there could be a sea of Green in London after the May local elections.
'There is a desire for radical change and deep concerns over the cost of living.'