An MEP who last year asked why doctors should perform gender reassignment surgery but not ‘gay cure’ therapy has suggested gay marriages will lead to incestuous and polygamous unions.

Roger Helmer MEP’s wrote on his blog, Straight Talking, that Cardinal Keith O’Brien’s comments about “grotesque” plans to introduce gay marriage were “impressive” and “brilliant”.

Helmer defected to UKIP from the Conservative party four days ago having previously said he would stand down from the European Parliament over his disillusionment with the party.

Of the Cardinal’s comment that gay marriage was ‘a grotesque subversion of a universally accepted human right’, Helmer continued: “I wish I’d thought of the phrase. Perhaps he ought to be a politician.”

Helmer, who once described the Catholic church as ‘systematically paedophile’ wrote yesterday: “Archbishop Keith O’Brien also makes the point, quite reasonably, that once you start to tamper with the institution of marriage, you get into some very murky water indeed. If two men can be married, why not three men? Or a two men and a woman?

“He could have gone further. Why not a commune? If two men have a right to marry, how can we deny the same right to two siblings? Are we to authorise incest?”

In the same blog post, Helmer also wrote: “I believe that Christian moral principles are not a bad basis for a free and fair society (even if I don’t always live up to them).”

Helmer stood down from the Conservative party in 2011 and joined right-wing UKIP four days ago.

At the begining of 2011, he had tweeted: “Why is it OK for a surgeon to perform a sex-change operation, but not OK for a psychiatrist to try to ‘turn’ a consenting homosexual?”

Although had had pledged to stand down, he later announced he would be completing his term in office with UKIP. He told BBC News: “UKIP better represents the views of Conservative voters than David Cameron’s Conservative Party.”

Nigel Farage, the UKIP leader, said: “A senior MEP from the Conservative Party, like Roger Helmer, defecting to us sends a message that people are taking UKIP very seriously.”

When he was the Conservative MEP for the East Midlands in 2009, he wrote on his blog: “‘Homophobia’ is merely a propaganda device designed to denigrate and stigmatise those holding conventional opinions, which have been held by most people through most of recorded history.

“It is frightening evidence of the way in which political correctness is threatening our freedom.”