UKIP has defended allowing a Polish politician criticised for a comment on hitting women into its grouping in the European Parliament.
Robert Iwaszkiewicz's decision to join the EFDD group means it has members from enough countries to increase its funding and presence in the parliament.
Leader Nigel Farage said Mr Iwaszkiewicz had made a "joke" and did not appear to be an "extremist".
UKIP added that parties had to co-operate in Europe to form groupings.
The Eurosceptic EFDD - Europe of Freedom and Direct Democracy - headed by Mr Farage, was thrown into disarray last week when one of its members, a Latvian MEP, left.
This took it below the European Parliament's threshold for forming a political grouping, which is to have at least 25 MEPs from seven different countries.
Mr Iwaszkiewicz's decision to join means the EFDD can retain the extra funding and ability to speak in the parliament that comes with the increased status.
He recently caused controversy in Poland after telling a newspaper that men hitting their wives can "help them come back down to earth". He later claimed he was being sarcastic.
He is a member of the Polish Congress of the New Right, led by Janusz Korwin-Mikke, who has a reputation for anti-EU rhetoric and controversial views about women.
According to Polish radio, Mr Korwin-Mikke said in June that French National Front leader Marine Le Pen had judged his party "too extreme" to be an ally in Europe.
UKIP emphasised that Mr Iwaszkiewicz was joining the EDFF group in a personal capacity and that it had no association with Mr Korwin-Mikke.
Board of Deputies of British Jews vice-president Jonathan Arkush said: "The board is gravely concerned by reports that UKIP may sit in the same parliamentary grouping as a far-right Polish MEP in a bid to save its funding.
"Robert Iwaszkiewicz belongs to an extremist party whose leader has a history of Holocaust denial, racist remarks and misogynistic comments."
For Labour, shadow Cabinet Office minister Michael Dugher said: "This shows once again that UKIP do not share the values of decent working people in Britain."
But Mr Farage said: "I have found nothing in this guy's background to suggest that he is a political extremist at all. He has joined our group to save us."
He told BBC Radio 4's World at One: "If our group doesn't have a voice then every single frontline spokesman will support the new European Commission."
Asked about Mr Iwaszkiewicz's comment on women, he replied that it had been meant as a "joke".
Questioned on why he had joined the EDFF group, Mr Iwaszkiewicz said: "Obviously Mr Farage is famous and well known not only in the parliament, but also in Poland.
"The decision to switch over to him was motivated by the intention to help out the only well-organised Eurosceptic group. It's giving a helping hand to the EFDD group."
On his comments about hitting women, he said: "Of course this was also twisted by the media. What I said wasn't the same as what appeared in the press. Of course, myself as well as my party are against family violence. I don't see where the problem is."
UKIP deputy leader Paul Nuttall told BBC Two's Daily Politics the comment was "not acceptable", but said: "He's said that he said it as a joke and it was misconstrued by the Polish media."
Mr Nuttall, speaking from Brussels, said the nature of the European Parliament, with the need for parties to join larger cross-national groups to get a better hearing, meant having to "cooperate with people you wouldn't necessarily cooperate with in the UK".
He added: "That's the nature of European politics. It's not like the UK. Unfortunately it's realpolitik out here."
Mr Nuttall said: "I'm proud that the group still exists. If it didn't exist there would be no Eurosceptic group in the European Parliament."
The EFDD has 48 members - half of them UKIP politicians - in the 751-seat parliament. In total, Eurosceptics account for about one-third of MEPs.
Mr Farage has blamed European Parliament President Martin Schulz for the departure from the EFDD last week of Latvian MEP Iveta Grigule. He accused Mr Schulz, a German Socialist, of "manipulative backroom politics of the worst kind".
Ms Grigule explained why she had left, saying: "I do not find it acceptable that MEPs turn their backs on the European anthem or the flags of member states."
She added that she objected to "shouting or rude remarks" in the chamber and had "warned Farage that, if nothing changes in this attitude, I will leave the group".
Mr Schulz has denied any wrongdoing in connection with Ms Grigule's decision.