UK Independence Party leader Nigel Farage has complained of verbal abuse and criminal damage against his supporters in the Wythenshawe and Sale East by-election campaign, which he said had been "as dirty as they come".
Mr Farage said the level of abuse directed at Ukip workers by people who he claimed were activists from Labour and the British National Party had been so high that police had been called four times.
He said the party's offices had been vandalised with foul-mouthed graffiti branding Ukip "Nazis", and a generator and bundles of leaflets were stolen, and claimed that individuals wearing red rosettes shouted at pensioners who said they were voting for Ukip.
Voting takes place tomorrow in the by-election to choose a replacement for Labour MP Paul Goggins, who died last month. Polls suggest Labour is heading for a comfortable victory, with Ukip hoping to snatch second place from the Conservatives.
Writing in The Independent, the Ukip leader claimed that Labour and the BNP behaved as if they "owned" certain sections of the working-class. He claimed council house residents were told to take down Ukip posters, because they should not be displayed on "our houses".
"This is a situation which political parties should be ashamed of," said Mr Farage. "People fought and died for our liberty and democracy and we must not ever allow politics to be tainted by such poor and in some cases criminal behaviour, where free and fair campaigning is distorted by threats of violence and damage.
"It is something that particularly emanates from the left. Far from being the party of the people, the party of the workers, the party of the ordinary men and women of the UK, the left wing risks - particularly at grassroots levels - becoming a movement that uses the sort of bullying it feigns to oppose in big business and among the elite."
A Labour Party spokesman said: "Nigel Farage's wild accusations are nonsense and a desperate smear to distract attention from the issues. Ukip are silent on Wythenshawe Hospital and offer no answers for the people of Wythenshawe and Sale East."