Labour’s vote share collapsed by 27.9%, while the Tories lost 17.6%.
It indicates that Reform is on course to spark a political earthquake at the May local elections, in which a polling expert predicts it could win a staggering 2,260 seats.
Zack Polanski’s Green Party is likely to be a huge beneficiary, boosting its numbers on councils across the country by about 450, according to leading psephologist Steve Fisher.
If his predictions come true, Reform UK’s gains would dwarf those of Labour under new leader Tony Blair in 1995.
In that year, Labour won 1,661 seats, paving the way for a landslide General Election victory two years later.
By contrast, the backlash against Sir Keir after a series of scandals could make 2026 Labour’s worst defeat on record.
The Prime Minister and his party have tanked in the polls after a series of controversial policies and U-turns, including on winter fuel payments and inheritance tax changes for farmers.
His premiership is said to be on the line after the Mandelson scandal, with questions raised over the PM’s judgement after he appointed the Labour peer as ambassador to the US despite his links to paedophile financier Jeffrey Epstein.
A bad set of local election results in May could heap further pressure on Sir Keir to quit, critics have warned.
