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There was a time when UKIP appeared bomb proof.

Candidates and party members would say offensive things. A media storm would hurtle through. And the party could steadily continue to win votes.

Supporters saw these rows as confected nonsense from a metropolitan media that did not like UKIP.

But things have changed. The party appears to have reached a plateau in the early to middle teens in the opinion polls.

To win new supporters, it now has to appeal more to women, students, middle class voters and of course black and ethnic minorities.

UKIP's problem is that some of these voters think the party has a racist tinge.

A YouGov poll last October found that 41% of voters thought UKIP a racist party and 55% thought it more likely to have candidates with racist views.

That is why UKIP is now more sensitive about accusations of racism and more ruthless in its disposal of candidates who say the wrong thing.

And that is why Nigel Farage has backed away quickly from his assertion in a Channel 4 documentary that much of Britain's race and other anti-discrimination laws should be scrapped.

It is one thing to talk of giving British jobs to British workers in a Britain outside the EU. It is quite another to suggest getting rid of laws that stop workers being discriminated against because of the colour of their skin.

Pollsters suggest that some disaffected Tory and Labour voters are attracted to UKIP but hesitate because they do not quite see the party as respectable enough. Today may have added to their doubts.