The decision of the Tories to join a new “anti-federalist” political group in the European Parliament, including a homophobic party, will give them more political clout, it has been claimed.

Timothy Kirkhope, acting chairman of the new European Conservatives and Reformists Group and Tory leader in the last European Parliament, said that rather than marginalising them, the new bloc will be “a powerful vehicle to drive forward our ideals”.

The 55-member bloc, including 26 Tory MEPs, is thought to be the fourth largest in Europe.

David Cameron’s choice to leave the more moderate EPP alliance has attracted criticism, especially as one group in the bloc is the Polish Law and Justice Party, whose leader Jaroslaw Kaczynski said in 2008: “The affirmation of homosexuality will lead to the downfall of civilisation. We can’t agree to it.”

Shadow foreign secretary William Hague tried to defend the Polish party, saying accusations of homophobia were “out of date and ill-informed”.

However, Konrad Szymanskitold, a Polish Law and Justice Party MEP, told newspaper Rzeczpospolita this week: “Law and Justice has a clear stand on this issue – we are against both homosexual marriages and the adoption of children by gays and lesbians. That is how our Euro MEPs will always vote.

“If some Tories happen to have a different view on this, then this grouping will not be voting unanimously on these issues…..”

Addressing the Association of British Insurers in London, Kirkhope said the bloc would provide a “lasting and reliable coalition against socialism and overregulation”.

He continued: “I believe that the new group will be a powerful vehicle to drive forward our ideals. I am aware that our political opponents have argued the reverse – that in parting company with the EPP we have diminished our influence in the EU.

“But the facts are already proving them wrong and I want to put the record straight. My experiences in recent days already demonstrate the increased leverage the British Conservative Party will now enjoy in EU decision-making.

“Conservative MEPs have now fulfilled the commitment we gave to the British people to create our own anti-federalist, centre and centre-right mainstream grouping in the European Parliament.”