Racist and homophobic statements have been caught on film during a campaign meeting for the right-wing populist British Reform Party.
Leader Nigel Farage says he is "appalled".
Strong condemnations are also heard from the Prime Minister's office.
In a clip filmed by an undercover reporter for British Channel 4 News, a campaign worker in Farage's constituency Clacton-on-sea is heard making racist statements about Britain's Prime Minister Rishi Sunak, whose parents are Indian.
He calls Islam "a sect" and suggests that mosques should be converted into pubs. To a voter, he suggests that asylum seekers who cross the English Channel "should be shot".
On the film, a party colleague is also heard mocking the Pride flag and calling homosexuals "nonces", a British slang term for sex offenders.
The revelation comes as Farage has fallen back in opinion polls ahead of Thursday's election, after saying in an interview with BBC that the Western world "has provoked" the war in Ukraine.
Earlier this spring, the Reform Party has made strong progress and Farage is seen as a challenger to the sitting Tory candidate Giles Watling in Clacton-on-sea.
Farage writes in a statement that he is "appalled by the comments from a handful of people connected to my campaign".
Prime Minister Rishi Sunak is outraged after the racist attack.
It hurts and it makes me angry, and I think he (Farage) has some questions to answer, says Sunak, according to AFP.
