Jewish leaders have told senior Conservatives to prove that the party vetted its new rightwing allies in Europe before it joined forces in the EU parliament with Polish and Latvian politicians accused of antisemitism.
Mark Francois, the shadow Europe minister, held an emergency meeting yesterday with Vivian Wineman, the president of the Board of Deputies of British Jews, after the Tories suggested that his organisation was politically motivated in raising concerns about the party's new allies.
Wineman wrote to David Cameron this week expressing concern at the past political activities of Michal Kaminski and Roberts Zile, and a meeting followed on Wednesday.
The Tories have now been asked to give details of where "due diligence" was exercised before the alliances were formed. The move indicates a hardening of the board's position. Last week it said it had looked into Kaminski and found nothing objectionable in his background.
A Tory aide said it was a "very friendly and constructive meeting".
The row over the alliances overshadowed the Tory conference, after the party invited both men, accused of links to antisemitic and homophobic political parties, to speak at a fringe meeting held on the same day as the party's first-ever gay pride night. Ben Summerskill, the head of the gay organisation Stonewall, pulled out of the pride event in protest.
Kaminski is the leader of the Tories' new grouping in the European parliament – the European Conservatives and Reformists. Zile is the leader of the Latvian For Fatherland and Freedom party.
The pair were singled out for attack a week earlier by the foreign secretary, David Miliband, at the Labour party conference, when he referred to Kaminski's "antisemitic, neo-Nazi" past and alleged that Zile's party conducted annual commemorations of the Latvian branch of the Waffen-SS.
Speaking at the Labour conference in Brighton, Miliband said that the Latvian party "celebrates the Latvian Waffen-SS with a march past of SS veterans" every year. "It makes me sick. And you know what makes me sicker? No one in the Tory party batted an eyelid," Miliband said.
Lord Janner, chairman of the Holocaust Education Trust, who was a war crimes investigator during his national service, told the Guardian: "My relatives in Latvia were all murdered by the Nazis and I think it is appalling that anyone would so much as say a good word about the Waffen-SS and those who today follow in their trail.
"It is vile that members of this party have marched in honour of their memory."
Zile told a fringe meeting in Manchester that he expected such attacks "to come from Moscow or the Kremlin, as it does from time to time".