Reform UK has picked up four new councillors in local by-elections, winning seats from both the Conservatives and Labour.
Nigel Farage’s party swept to victory in polls in Rotherham, Tewkesbury, Bassetlaw and Hartlepool on Thursday.
The council seats are in key target areas for Reform at the next general election.
Ashford MP Lee Anderson singled out the Ranskill ward win on Bassetlaw council, describing it as a “huge gain from the Tories in their safest seat”.
Labour was ousted in Throston ward in Hartlepool with Reform taking 48.7% of the vote.
Sir Keir Starmer’s party also lost the seat it was defending in Keppel ward in Rotherham as Reform won 40.3% of the vote. Labour’s share fell by over 13 points, with the party finishing in third place.
It comes just a week after Reform lost two by-elections called when the party’s councillors quit days after being elected.
The Liberal Democrats and Tories won council seats in Nottinghamshire and Durham that Mr Farage’s party had claimed in May’s local elections.
Keith Girling reclaimed the Newark West division on Nottinghamshire council for the Conservatives by just eight votes after Reform’s Desmond Clarke stepped down in the seat less than a week after being elected on May 1.
Mr Girling said his win showed that the Tories “aren't dead”, but slammed his predecessor for wasting money as he claimed that rerunning the election had cost almost £25,000.
Reform made huge gains and seized control of eight local authorities in May.
The party won 677 seats across the country, cementing it as a prime challenger to Labour and the Tories.
It also beat Labour in the Runcorn and Helsby parliamentary by-election to make Sarah Pochin its fifth MP.
However, Reform MP James McMurdock has since been suspended and this week said he will not return to the party following questions about loans he took out under a Covid support scheme.
The claims, published by the Sunday Times, relate to £70,000 Mr McMurdock secured via two companies, and whether the firms were eligible.
Responding to the investigation, the Essex MP said all his business dealings had been in line with the rules.
But he added that he had asked to be suspended from the parliamentary party as a "precautionary measure".
On Tuesday he said that after taking legal advice he would “continue my parliamentary career as an independent MP".
