Nigel Farage is a racist, Labour MP David Lammy claimed today in a departure from remarks made by his party leader Ed Miliband.
Shadow home secretary Yvette Cooper has also referred to Mr Farage's comments as racist, while senior MP Dianne Abbott has said she is "glad everybody has stopped pussyfooting around".
Mr Miliband condemned the racial slur as "completely out of order" but said politics was "disagreeable enough without political leaders saying about other political leaders 'they are a racist'".
Prime Minister David Cameron has also stopped short of saying the Ukip leader was racist, despite describing his remarks as "pretty unpleasant".
Mr Farage has faced a storm of criticism following an interview on LBC radio last week where he suggested there was a difference between how people should feel if Romanian or German people moved in next door.
Ukip took out a full page advert in the Daily Telegraph, forming an open letter to the British public insisting it was not a racist party.
But speaking on the BBC 2 Daily Politics programme, black MP Mr Lammy rejected the assertion.
He said: "I am from a background where my parents arrived here as immigrants. I remember a context in which some people said you don't want these people living next to you. That was racist.
"What Nigel Farage said over the weekend was racist, so I'm clear, he's a racist.
"'He is leader of a national party. He should not be slurring whole communities of Romanians who come to this country and describing them as somehow bandits, criminal. It's deeply, deeply nasty.
'We must take that kind of slur extremely seriously, that's the bottom line."
Ms Cooper told ITV: "It's not racist to be worried about immigration or to want stronger controls, but it is racist to somehow stir up fears about Romanians living next door. So Ukip should say they were wrong on that."
Ms Abbott, a former shadow health minister, told the Guardian "his remarks were racist" and she was "glad everybody has stopped pussyfooting around".
In a BBC interview earlier, Mr Cameron said: "I think he has said in recent days some really pretty unpleasant things and he has even himself had to admit he got it wrong.
"I will leave others to judge but what I have heard from some of the candidates, some of the donors to the party is a succession of pretty appalling things.
"I would just say to people look, what we need in Britain is not the politics of anger, we need the politics of the answer - how do we get migration better under control, how do we reform our welfare, how do we get the relationship right with Europe.
"I am offering solutions, I am offering a plan, a plan that is working with our economy, and people should veer away from some of these statements."
Labour leader Ed Miliband described Mr Farage's original comment on Friday as a racial slur that was "completely out of order".
Mr Miliband said he could understand why people supported Ukip because they are not happy with the political system, but he stressed Mr Farage's party do not have the solutions.
He told BBC Radio 4's Today programme: "I think, though, our politics is sort of disagreeable enough without political leaders saying about other political leaders 'they are a racist'.
"I think it was deeply offensive, I think it was wrong what he said."
In its newspaper advert, Ukip insisted it was not racist but repeated its warning about the risk posed by organised criminal gangs from Romania.
Mr Farage said his comments about people being right to be concerned if a group of Romanian men moved in next door had caused a "predictable storm of protest and accusations of racism".
The Ukip leader initially stood by his remarks, which came during a bruising interview with LBC, but last night he said: "Do you know what, in life sometimes people get things wrong."
He told BBC News: "I regret the fact that I was completely tired out and I didn't use the form of words in response that I would have liked to have used.
"I should have just hit back immediately and said: 'Look, understand there is a real problem here - you can't deny it - too much criminality from these gangs has come to London'."
In an advertisement in The Daily Telegraph taking the form of an open letter from Mr Farage, the Ukip leader said: "Let me be clear - Ukip is not a racist party, and our immigration policy, far from being racist, aims to end discrimination against non-Europeans.
"The vast majority of Romanians who have come to the UK wish to better their lives and would make good neighbours.
"But there is a real problem, an unpalatable truth that our political class would rather not discuss. Since the welcome fall of Communism and the awful dictator Ceausescu, Romania has struggled to complete a full transition into a western democracy."
There was discrimination against the Roma minority and a "huge problem" with the growth of criminal gangs, he said.
Mr Farage claimed European Union free movement rules meant there was "nothing the UK authorities can do to stop such people from entering our country".
He said: "We should not be in a political union with Romania, with an opened door to all of their citizens."
By leaving the EU and "taking back control of our borders" the "necessary checks" could be done on would-be immigrants.
"When this happens my answer to the question 'should people be concerned if a group of Romanian men moved in next door?' will be 'no'."
In a new BBC interview, Mr Farage said he did not say people "should" be concerned about Romanians moving in next door, just that they "would".
He said: "I want to change that so people wouldn't be concerned, and we can do that by getting back proper border controls.
"There are lots of Romanians who want to come to Britain and work and do good things for the country."
Mr Farage said it would not be acceptable for people to express concerns about Jamaicans, Nigerians or Irish people moving next door.
He said: "Can we just have an honest appraisal of what has happened to post-communist Romania?"
The latest poll on Thursday's European elections showed Ukip's lead almost halving since the end of last month from 11 points to six.
Among those certain to vote, ComRes found it had 33% of voters - down five points - to Labour's 27%, the Conservatives' 20% and the Liberal Democrats' 7%.
The survey, for ITV News, also found Mr Farage was the party leader most likely to be considered "weird" - 31% choosing him over Ed Miliband (23%) or David Cameron (7%).
And he lagged well behind on trust - only 10% picking him as the most trustworthy, compared with 17% for each of the main party leaders.
ComRes interviewed 2,061 adults online between May 16 and 18.
Ms Abbott told Channel 4 News that Mr Farage was using a "very chilling and classically-racist line" but said questions about whether Mr Farage was himself a racist were "something of a red herring".
"There is no question that his comments about not wanting Romanians living next door are racist," she said, d rawing parallels with attitudes that saw her father unable to rent a house in an affluent area of London in the 1970s.
"The issue is not whether he personally is a racist. The issue is whether the remarks were racist and whether he is running a party that doesn't scruple to use racism and xenophobia to attract voters."
Parties did not want to "call it out" as racism for fear of not being able to attract back voters who were backing Ukip on Thursday, she suggested.
Britain is "less racist than it has ever been" but economic worries have made people more likely to be seeking immigrant scapegoats.