From a former police station in a small English town, a handful of right-wing campaigners used little more than a WhatsApp group to mount a challenge to the century-long dominance of Britain's big two parties at last year's election.

The ramshackle operation secured the populist Reform U.K. party the third-biggest vote share and five parliamentary seats. It also convinced its leader, Brexit veteran Nigel Farage, he had to professionalize the party, and fast.

Now a predicted big win for Reform in Thursday's local elections could see it become a credible right-wing force that could overtake the long-dominant Conservatives to become the main challenger to the governing Labour Party at the next national election.