Labour and Conservative polling is showing that attacks claiming Nigel Farage is a racist have backfired since voters do not regard him as such and see the assaults as a sign members of the political establishment are ganging up to undermine him.

The apparent backlash is coming to both parties from telephone polling and focus groups, which say that the attacks have raised Farage's profile and confirmed him as the anti-establishment candidate. It does not tally with published opinion polls that show the Ukip lead in the European elections narrowing slightly.

One source said: "Calling people names does not work. It confirms the old politics."

The findings on the penultimate day of campaigning before Thursday's European and local elections are especially acute for the Labour party, which has been locked in an internal battle about how aggressively to attack Farage. Ed Miliband has studiously not called him a racist and tried instead to offer policy solutions to the issues driving the Ukip vote. Other strategists within the party are arguing that only a more direct attack will bear fruit with traditional Labour voters.

The row over whether Ukip is racist spilled into the streets on Tuesday when Farage failed to attend his own mini-street carnival in Croydon, south London, after it descended into bitter rows and one of his local candidates, Winston McKenzie, described the area as an unsafe "dump".

A man argues with anti-Ukip protesters at a party rally for the European and local elections in Croydon. Photograph: Sang Tan/AP

The event was organised after a series of controversies over allegedly racist comments made by Ukip candidates and Farage's suggestion that people might not want to live on a street with Romanians.

Farage later insisted the organisers of the event had wanted him to go but he "didn't have time" and was busy.

Ed Miliband on ITV's Good Morning Breakfast. Photograph: /ITV

At a rally later in Eastleigh, Hampshire, Farage quoted Gandhi as he dismissed criticism of his party by the political establishment and media. "First they ignore you, then they laugh at you, then they attack you … then you win," he said, predicting that Ukip would definitely come first in the European elections.

Miliband had his own personal nightmare when he appeared on BBC Wiltshire and tried to bluff his way out of the fact that he did not know the name of the Labour leader on the local Swindon council, one of Labour's key target councils.

He also looked uncomfortable when he appeared on morning TV and was asked how much he spent on groceries in a week.

The chancellor, George Osborne, is planning to mount an eve-of-poll attack on Labour and Ukip urging the country to "reject the forces of pessimism on the left and the populist right".

In a speech to the CBI on Wednesday he will say: "Political parties on the left and the populist right have this in common: they want to pull up the drawbridge and shut Britain off from the world.

"They want to set prices, regulate incomes, impose rent controls, wage war on big business, demonise wealth creation, renationalise industries – and pretend that they can re-establish control over all aspects of the economy. Whether from the left or the populist right, we now see a deeply pessimistic, depressing, anti-business agenda.

"It takes advantage of the understandable anxieties of a population unsettled by the pace of globalisation, and peddles a myth that Britain can stop the world and get off."

Farage's Ukip Croydon event started to go wrong when two members of the steel band hired to provide a carnival atmosphere said they were uncomfortable and had no idea they would be playing for Ukip.

Ukip candidate Winston McKenzie, right, speaks to a woman at the Croydon event. Photograph: Sang Tan/AP

Marlon Hibbert, 22, whose parents are Jamaican, said he thought Ukip was racist and he was upset about the booking. "They are something I don't like the idea of," he said. "My parents came over here to work. Our country is for everybody with opportunities for everyone."

Fellow musician, 16-year-old Kishan Shorter agreed, saying he was not happy with Ukip's views.

As the band played for a short while, one of the party's most prominent black activists, Winston McKenzie, a Croydon council candidate, used a loud-hailer to say he was proud to be a supporter.

But he was interrupted by two protesters, who claimed to be from Romania and declined to give their names, accusing Ukip of being a Nazi party and holding a banner saying "Nigel Farage Racist Scum".

Farage and Ukip were defended by several candidates from ethnic minority backgrounds, including Rathy Alagaratnam, who is standing in Merton. The former Labour activist, who tried to take her former party to a tribunal for racial discrimination, said accusations of racism against Ukip were "an excuse because people do not want to debate the European question".

Marjorie King, a black Ukip candidate in north Croydon, said she did not think Farage was racist and had not seen his comments about Romanians. She said she was attracted to Ukip because it was the only party "standing up for Christianity".

Asked whether Farage was frightened of attending, McKenzie, standing in Croydon North, explained : "If he hasn't turned up he is a very sensible man. Croydon, which was once the place to be, the place to shop, has now become sadly a dump … How can you ask an international leader to turn up somewhere where he feels unsafe?"

Labour will be reviewing how it is briefing Miliband after he stumbled on radio and television.

He ran into trouble when he was asked on BBC Wiltshire for his views of Jim Grant by the presenter Ben Prater, who stopped short of mentioning that he is the leader of the Labour group on Swindon borough council.

"You will enlighten me I'm sure," Miliband said when he was asked by Prater whether he knew who Grant is.

Miliband then wrongly described Grant as the leader of the Tory-led council. "Well he is doing a good job as leader of the council – Jim is. And I think that is the case."

When Prater pointed out that Grant is not leader of the council, Miliband said: "Well, I think he is doing a good job for Labour on the council. He is doing a good job for Labour on the council."

Miliband's awkward radio interview came after he said he was well placed to focus on the cost of living crisis in Britain even though he appeared to underestimate his family's weekly grocery bill.

The Labour leader, who said it was right to place the issue at the front of his general election campaign even though he is "relatively comfortably off", told ITV's Good Morning Britain that his family spent at least £70 to £80 a week – and probably more – on groceries.

When he was told that the average weekly bill for a family of four was more than £100, he said: "Right, well it [the grocery bill] is more than £100."

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