A Ukip council candidate who posted an offensive tweet about the comedian Lenny Henry resigned his membership of the party after it was "mutually agreed this would be the best course", a Ukip spokesman said.
William Henwood, who suggested Henry should emigrate to a "black country", was due to stand for the party in next month's election in Enfield, north London.
Labour voters are defecting to Ukip because the party has become "very middle class", a former adviser to Ed Miliband has said.
Lord Glasman, who was made a peer by Mr Miliband, said Ukip's success would hit Labour "in the heartlands".
He told The Times that the last election saw a sharp decline in Labour's traditional working class base.
"The Labour middle class vote held up (in 2010). It was the working class vote that died. These are often people who are earning, who have jobs, but they don't see Labour as representing their interests."
Bad publicity surrounding the UK Independent Party is having no affect, the party's deputy chairman told ITV News. Neil Hamilton said that it showed the "difference between ordinary, normal people in the country, and those in the 'Westminster bubble'".
Mr Hamilton added that claims surrounding Ukip candidate William Henwood would be investigated, and that if he made "false statements" over the reported racist remarks, he would be "turfed out".
Any breach of our rules will be duly investigated and action will be taken.
However one has to question why the other parties are spending hours behaving like secret police and trawling through the social media of Ukip candidates who are everyday men and women, rather than actually doing politics.
Perhaps if they did they would be better able to tackle us on policy, rather than having to rely on smear campaigns to try to undermine Ukip's increasing popularity.
Were we to return the favour we would find an even greater wealth of embarrassment and disgrace in the other three parties' ranks to also spread across the media.
Ukip is facing a fresh backlash over comments made on Twitter by one of its candidates who suggested Lenny Henry should emigrate to a "black country" in response to a speech by the actor and comedian that said ethnic minorities were under-represented on British television.
William Henwood, who is standing in a council election, told the BBC: "I think if black people come to this country and don't like mixing with white people why are they here? If he (Henry) wants a lot of blacks around go and live in a black country."