The Liberal Democrats would not form a coalition government with the Conservative Party after the 2015 general election if Ukip formed part of the group, according to Nick Clegg.
The Liberal Democrat leader criticised Nigel Farage's party for representing the "politics of fear, the politics of blame and the politics of vilifying foreigners".
"Compromising with a party that wants to turn the clock back to the 1950s; has a very regressive attitude towards women; that has at best a very ambivalent attitude to the NHS. I just cannot see the Liberal Democrats and Ukip in the same political space," the Sheffield Hallam MP said.
The comments come after Ukip won the Rochester and Strood by-election and secured its second MP – Conservative defector Mark Reckless.
The opinion polls have recently put Labour and the Conservatives neck and neck ahead of the general election next May.
The figures means one party may not be able to gain a majority of MPs in the House of Commons after the vote and smaller parties, such as the Liberal Democrats and Ukip, could be needed to form a coalition government.
But the Deputy Prime Minister told IBTimes UK earlier in the year that he would work with Farage on a cross-party consensus on the future of the UK's industrial policy.
Clegg said he would welcome Ukip into the consensus under the right conditions.
He said: "I think we should work with whichever party that's prepared to commit, as we've had, to a long-term strategy, which is an essential ingredient in the long-term fortunes of British manufacturing.
"Ukip doesn't have any MPs in Westminster and I don't even think Ukip is going to claim it's going to be part of any future British government, but in a sense the more the merrier."
The Liberal Democrat leader also criticised Labour's former shadow attorney general for posting a picture on social media site Twitter of a house with three England flags and a white van.
Emily Thornberry posted the tweet as voters went to the polls in Rochester and Strood.
Clegg said the tweet was a "drippingly patronising thing to do – maybe it is what happens when you become MP for Islington".
He said: "I just thought it was a jaw-droppingly condescending way of treating someone who is just proudly hanging some flags outside their home. What is wrong with that?"