Tony Blair has warned Ed Miliband not to chase Ukip to win over voters and insisted curbing immigration would be a "disaster" for Britain.
The former prime minister said Labour must be "really careful" of saying things that suggested Nigel Farage's party are justified in their policies.
Mr Miliband last week announced that a Labour government would immediately bring in an immigration Bill and said the EU "needs to change if we are to deal with the problems of immigration".
Mr Blair said the way to tackle the threat from Ukip was to "deal with it by what you believe".
He told Progress magazine: "Let's be clear: We don't think that Ukip's right, not on immigration and not on Europe - so the first thing you've got to be really careful of doing is ... saying things that suggest that they're kind of justified in their policy because what you're actually going to do is validate their argument when in fact you don't believe in it."
Stopping immigration would be "a disaster for this country" and Labour must not "end up chasing after the policies of a party like Ukip, who you don't agree with, whose policies would take this country backwards economically, politically, in every conceivable way, and who, ultimately, at the heart of what they do, have a rather nasty core of prejudice that none of us believe in, which you've actually got to take on and fight. So the way to deal with this is to deal with it by what you believe".
Mr Blair claimed the way David Cameron is dealing with the threat from Ukip "doesn't do them any electoral favours at all".
He claimed the Tories would be better off at the ballot box "if they actually stood up against these people and said 'you don't understand the way the world works today, your policies will take us backwards and we're not going there'."
Mr Blair added: "There's a huge desire in a large part of the media in this country to return British politics to a traditional Tory party fighting a traditional Labour party."
That would lead to a "a traditional result", he warned.