David Cameron has been under fire for dismissing the UK Independence Party (Ukip) as a party of "fruitcakes, loonies and closet racists", in a now-notorious radio interview in 2006.

However, he may have won support from an unusual quarter - the founder and former leader of Ukip, Professor Alan Sked, says the party he launched in 1993 has become "extraordinarily right-wing" and is now devoted to "creating a fuss, via Islam and immigrants. They've got nothing to say on mainstream issues."

"Its extraordinary," Sked told the HuffPost UK, "that at the last general election, with the country facing the greatest economic crisis since the Great Depression, [Ukip's] flagship policy was to ban the burqa."

"They're not an intellectually serious party. Their views on immigrants and on [banning] the burqa are morally dodgy."

Sked, who led the party between 1993 and 1997, before quitting and resigning his membership, said it was a Ukip peer who invited Dutch politician Geert Wilders to the UK to screen his anti-Islam film Fitna in October 2009. In recent years, several Ukip politicians and candidates have been caught out making both anti-Islam and anti-Muslim remarks: former party leader Lord Pearson claimed Muslims were "breeding ten times faster than us"; one Ukip parliamentary candidate denounced "Muslim nutters who want to kill us and put us under medieval Sharia law" and another described Islam as "morally flawed and degenerate" and endorsed Wilders' view of Islam as a "retarded ideology".

Professor Sked, a specialist in international history at the London School of Economics, told the HuffPost UK that he "understands" - though disagrees with - the "rationale" behind the recent decision by social workers in Rotherham to remove three ethnic minority children from the home of two foster parents, on the grounds that they were members of Ukip.

Asked if Ukip is a xenophobic party, he replied: "It seems to be anti-Islam and anti-immigrant. If that adds up to xenophobic, then yes."

Sked was careful not to label all Ukip voters or members as xenophobes or Islamophobes: "There are thousands of broad-minded people in the country who want to get out of the European Union and [Ukip] seems to the only party they can vote for."

A Ukip spokesman rejected Professor Sked's claims and told the HuffPost UK: "We have no views on 'immigrants'. We have views on mass immigration but not on immigrants themselves. Alan is a decent chap and an academic but has had nothing to do with UKIP for 15 years. He knows not of what he speaks and retains a long-term bitterness towards the party."

The spokesman added that the party's policy on the burqa "had been dropped and not yet rewritten".

The former Ukip leader's comments, however, were bolstered by academic Robert Ford, of Manchester University, who has conducted extensive research into the views and backgrounds of the party's voters.

Ford told the Huffington Post: "Our research - which includes the most comprehensive analysis of the attitudes of Ukipsupporters ever conducted - shows that Ukip supporters... are more likely than supporters of any other party except the BNP to hold hostile attitudes about immigrants and ethnic minorities. UKIP supporters are more likely to agree that the government should repatriate immigrants, and allow employers to favour white job applicants. Ukip supporters are also more likely to agree that Islam poses a serious threat to Western civilization, that local councils have favoured immigrant applicants for council housing and to believe that immigrants commit most crime."

It is clear, added Ford, that "Ukip appeals to British voters with negative views about immigrants, Muslims and ethnic minorities".