Michael Howard has refused to back down over his uncompromising stance on immigration, which has threatened to hijack the Conservative Party's wider political agenda.

The Tory leader was repeatedly questioned on his views on immigration at a press conference this morning which was supposed to focus on policing.

He was also forced to deny that a deputation of his own frontbenchers had asked him at the weekend to tone down his harsh rhetoric.

Mr Howard gave warning in a television debate last night that Britain could be torn apart by race riots if people believe immigration is out of control, prompting an angry response from some members of the audience.

His remarks to ITV’s Ask The Leaders programme last night drew comparisons with Enoch Powell’s infamous "rivers of blood" speech on immigration, and he was accused of pandering to race hate.

This morning he was taking a more cautious line, and stopped short of repeating his remarks. But he repeated that a belief that there were no proper controls spread "anxiety" which damaged community relations. Good community relations were reliant on controlling immigration, he said.

The row comes at a moment when Tory momentum appears to be faltering. Three polls published today show the Conservatives lagging behind Labour by between five and 10 percentage points.

Last night Rupert Murdoch, the chairman of News Corporation, parent company of The Times, criticised the Tory policy on immigration. The Government must stop people entering the country illegally, but should continue a policy of allowing legal immigration, Mr Murdoch said, in a media briefing during the Milken Institute conference in Los Angeles.

He backed Labour's proposed move to a points system, where potential new arrivals are assessed on the skills and education they have to offer.

According to one report, Shadow Cabinet members have become so concerned at Mr Howard's strident views that they asked him to tone down the rhetoric on asylum and immigration. The group made "representations" to Mr Howard’s office on Sunday afternoon, The Guardian reported today.

But Mr Howard denied it, saying: "We have had no such calls, either to me or to my office." And he stressed that he had no intention of changing course on the issue.

"We clearly believe that there should be a limit on immigration, that’s our view," he said this morning.

"I have always believed, I’m sure it’s true, that good community relations and firm but fair immigration controls go hand in hand together.

"We have seen immigration triple under Mr Blair. No one’s ever been asked their views about that.

"You can’t specify what might happen but I believe, as I’ve made clear very many times, that if we are to continue to have good community relations in this country you have to be vigilant.

"And if people lose confidence in the system and believe it’s out of control, I believe that breeds a sense of insecurity and that’s damaging to good community relations."

On last night’s ITV’s Ask The Leaders show, Mr Howard was asked if he feared a repeat of the race riots seen in Burnley and Oldham.

Mr Howard replied: "Yes. I think people have to have confidence in the system. They have to understand there is a proper system of controls and that gives people reassurance."

He insisted today he would continue to discuss the issue: "It’s one of our five priorities and I will continue to talk about it."

Charles Kennedy, the Liberal Democrat leader, criticised the stress that Mr Howard was placing on the issue of immigration. Mr Kennedy said that all parties proposed controls and accused Mr Howard of dodging sensible debate on the issue to appeal to his core vote.

Trevor Phillips, the Commissioner for Racial Equality, told The Times last week that the tone of the debate on immigration was sour and fractious. He said that the number of reported racial attacks had soared since the election campaign started, and warned politicians to be careful of their tone in discussing race issues.

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