The husband and wife, who have been fostering for nearly seven years, said they were made to feel like criminals when a social worker told them their views on immigration made them unsuitable carers.

The decision by Rotherham Metropolitan Borough Council has provoked widespread criticism, with campaigners representing foster parents describing the decision as “ridiculous” and warning that it could deter other prospective foster parents from volunteering.

But Joyce Thacker, the council’s Director of Children and Young People’s Services, today said the three ethnic minority children had been placed with the couple as an emergency and the arrangement was never going to be long-term.

She told the BBC Radio 4’s Today programme: “We always try to place children in a sensible cultural placement. These children are not UK children and we were not aware of the foster parents having strong political views.

“There are some strong views in the Ukip party and we have to think of the future of the children.”

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“Also the fact of the matter is I have to look at the children’s cultural and ethnic needs. The children have been in care proceedings before and the judge had previously criticised us for not looking after the children’s cultural and ethnic needs, and we have had to really take that into consideration with the placement that they were in.”

Asked what the specific problem was with the couple being Ukip members, Mrs Thacker told the BBC: “We have to think about the clear statements on ending multi-culturalism for example.

“These children are from EU migrant backgrounds and Ukip has very clear statements on ending multiculturalism, not having that going forward, and I have to think about how sensitive I am being to those children.”

She added that there was no issue about the quality of care the couple provided and said she would co-operate with any investigation.

The Labour Party, which runs Rotherham, today tried to distance itself from the council’s decision.

A spokesman for the party said: “Membership of Ukip should not block parents from adopting children. There needs to be an urgent investigation by Rotherham Borough Council into this decision.”

The couple, who do not want to be named to avoid identifying the children they have fostered, are in their late 50s and live in a neat detached house in a village in South Yorkshire.

The husband was a Royal Navy reservist for more than 30 years and works with disabled people, while his wife is a qualified nursery nurse.

Former Labour voters, they have been approved foster parents for nearly seven years and have looked after about a dozen different children, one of them in a placement lasting four years.

They took on the three children — a baby girl, a boy and an older girl, who were all from an ethnic minority and a troubled family background — in September in an emergency placement.

They believe that the youngsters thrived in their care. The couple were described as “exemplary” foster parents: the baby put on weight and the older girl even began calling them “mum and dad”.

However, just under eight weeks into the placement, they received a visit out of the blue from the children’s social worker at the Labour-run council and an official from their fostering agency.

They were told that the local safeguarding children team had received an anonymous tip-off that they were members of UKIP.

The wife recalled: “I was dumbfounded. Then my question to both of them was, ‘What has Ukip got to do with having the children removed?’

“Then one of them said, ‘Well, Ukip have got racist policies’. The implication was that we were racist. [The social worker] said Ukip does not like European people and wants them all out of the country to be returned to their own countries.

“I’m sat there and I’m thinking, ‘What the hell is going off here?’ because I wouldn’t have joined Ukip if they thought that.

“I’ve got mixed race in my family. I said, ‘I am absolutely offended that you could come in my house and accuse me of being a member of a racist party’.”

The wife said she told the social worker and agency official: “These kids have been loved. These kids have been treated no differently to our own children. We wouldn’t have taken these children on if we had been racist.

”The boy was taken away from them the following day and the two girls were removed at the end of that week.”

The wife said the social worker told her: “We would not have placed these children with you had we known you were members of Ukip because it wouldn’t have been the right cultural match.”

The wife said she was left “bereft”, adding: “We felt like we were criminals. From having a little baby in my arms, suddenly there was an empty cot. I knew she wouldn’t have been here for ever, but usually there is a build-up of several weeks. I was in tears, although not in front of the social worker.”

Her husband added: “If we were moving the children on to happier circumstances we would be feeling warm and happy. To have it done like that, it’s beyond the pale.”

The couple said they had been “stigmatised and slandered”. They now fear they will no longer be allowed to foster again.

Nigel Farage, the leader of Ukip, described the actions of Rotherham borough council as “a bloody outrage” and “political prejudice of the very worst kind”.

UKIP was once considered a single-issue fringe party but is now part of Britain’s political mainstream, with some recent national polls putting its support as high as nine per cent.

Its manifesto includes a demand for Britain to pull out of Europe and to curb immigration. It is also critical of multiculturalism and political correctness.

The party has three peers in the House of Lords, all defectors from the Conservatives, and 12 MEPs, although it has never won a seat in the Commons. It has a candidate in next week’s by-election in Rotherham.

Mr Farage said: “I am outraged politically and very upset for them. I think this is the kind of thing where we need some sort of decree from a Government minister that Ukip is not a racist party.

“This is political prejudice of the very worst kind. It is just a bloody outrage.”

He pointed out that Ukip has a black candidate in the forthcoming Croydon North by-election.

David Goosey, the chairman of the trustees at Community Foster care, an independent fostering charity, said: “If this is accurate and there are no other extraneous matters that have concerned the authorities, then it is completely ridiculous and no self-respecting authority should be stopping people fostering on the grounds of their membership of Ukip.”

Nushra Mansuri, of the British Association of Social Workers, said: “My first question would be, does the local council have a clear equality policy so you can understand a bit more about the decision-making?

“Otherwise it’s very difficult to fathom.”

Tim Loughton, the former children’s minister, said: “I will be very concerned if decisions have been made about the children’s future that were based on misguided political correctness around ethnic considerations.

“Being a supporter of a mainstream political party is not a deal-breaker when it comes to looking after children if it means they can have a loving family home.”

A spokesman for Rotherham council said last night: “After a group of sibling children were placed with agency foster carers, issues were raised regarding the long-term suitability of the carers for these particular children.

“With careful consideration, a decision was taken to move the children to alternative care. We continue to keep the situation under review.”