Ukip’s ability to vet its own election candidates has come under intense questioning after a series of embarrassing leaked emails, campaign trail blunders, and allegedly racist and homophobic comments from their would-be councillors ahead of local elections this week.

As leaked emails showed key figures in Ukip comparing the challenge of leading the anti-EU party to “herding cats” emerged today, the party’s leader, Nigel Farage, admitted they had been overstretched in assessing the suitability of some 1,700 candidates.

To compound matters, Northumbria Police confirmed tonight that it was investigating an allegation of postal fraud by the party in the Cowpen area of Blyth, Northumberland. Detectives said they had received a complaint and were in the early stages of an investigation.

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Private messages from the Ukip treasurer, Stuart Wheeler, and prominent MEP Godfrey Bloom, published in The Observer, suggested the party needed to buy policies “off the shelf” from think-tanks. Mr Bloom said he was worried about excessive “political correctness” among new recruits. Writing to Mr Wheeler, he said: “We are also attracting new members who bring main party ‘baggage’. Focus groups, quotas, even political correctness. We must be wary of listening to these siren voices. We did not get where we are today by following, but leading.”

It came as Mr Bloom – the Yorkshire and North Lincolnshire MEP who once joked he wanted to get involved in women’s rights issues because he did not “think they clean behind the fridge enough” – appeared to answer criticisms that he was a “misogynist” by posting pictures online of himself with groups of women alongside clips of him speaking on the BBC’s Woman’s Hour.

The party was forced to suspend an East Sussex candidate on Thursday after she was accused of being a “Holocaust denier” who claimed that the Second World War was engineered by Zionists hoping to create the state of Israel. Anna-Marie Crampton, who was standing for Ukip in Crowborough, East Sussex, claimed that someone had assumed her identity to write that the Second World War had been financed by Jewish “banksters [sic] to make the world feel guilty”.

Ukip yesterday confirmed it was investigating a handful of candidates over alleged links to far-right groups, homophobic and racist comments. A spokesman added that it did not condone “unpalatable views”.