A letter signed by celebrities such as Ewan MacGregor, Stephen Fry and Jo Brand has asked Tory leader David Cameron to oppose the views of his party’s new European allies.

Cameron broke away from an alliance with the EPP in Europe to honour an election promise he made but his new allies have been accused of homophobia, racism and anti-semitism.

The party has invited Polish Law and Justice Party MP Michal Kaminski, to speak at its conference this week. Kaminski was filmed calling gay people “fags” in an interview in 2000. He is now the president of the Tories’ new bloc in Europe, the European Conservatives and Reformists Group.

The Conservative Party is due to host a special gay event tonight in Manchester called Conference Pride.

The letter said: “It is not just that your new Polish allies oppose gay marriage and adoption but that their vile rhetoric – branding homosexuality as a ‘pathology’, gays as ‘perverts’, and describing ‘the affirmation of homosexuality’ as ‘the downfall of civilisation’ – was used to whip up hate during their election campaign.

“Your party’s decision to host an LGBT event at conference is a good step in the right direction.

“But it will seem empty – a two faced gesture – if in the same week you fawn over allies whose homophobia has no place in modern Manchester, in modern Britain, or in Europe.”

It added: “We want to believe the Conservative Party has really changed – please help us by rescinding the invite to the Polish Law and Justice Party and urging them either to change their views or quit your new European group.”

Others who signed the letter include Labour MEP Michael Cashman, NUS president Wes Streeting, Eddie Izzard and Patrick Stewart.