Norman Tebbit has labelled the prime minister’s reasons for supporting equal marriage ‘absurd’ and warned that ‘nests of snakes’ inhabit the ‘can of worms’ the country is about to open, suggesting polygamy and incest may naturally follow.

Blogging on the Telegraph website, Lord Tebbit wonders whether the move to allow gay couples to marry which was personally backed by David Cameron last year is “another contagion from his Lib Dem partners” and says it will not be a vote winner, since “the pink vote is substantially less than the UKIP vote”.

Gays, he adds, are “not a separate species” and “cast their votes on very much the same issues as the rest of us”.

On the legal changes necessary to secure marriage equality, Lord Tebbit writes: “Was anyone asked to check in how many pieces of legislation the words “husband” or “wife” appear? Are they to be replaced by some suitable non-discriminatory new word or words? Then what about the grounds for divorce? How will adultery be redefined? Exactly what kind of sexual acts outside marriage will constitute grounds for divorce? What will amount to the consummation of a marriage?”

The government’s public consultation addressing many issues regarding the introduction of equal marriage rights runs until 14 June this year.

The former Conservative party chairman continues in vivid metaphor: “Within the can of worms that Mr Cameron is determined to open there are several nests of snakes. Why should a marriage be confined to just two persons? What is the barrier to the marriage of sisters, brothers or even parents and children?”

Dismissing as “absurd” the prime minister statement that he supported equal marriage “because he is a Conservative”, he says “little thought” has gone into the proposal and adds: “He did not mention it when he set out his stall in the Conservative Party leadership election not long ago. Did he believe it then?”

In fact, as LGBTory pointed out this month, the Conservatives had included a pledge to consider equal marriage rights in their equalities manifesto shortly ahead of the general election and this was reported in the Telegraph, which hosts Lord Tebbit’s blog.

Last year Lord Tebbit said he did not “know where, apart from to a Big Society gay wedding in Westminster Abbey, the Prime Minister really wants to go…”

In a Lords debate on the 2007 Sexual Orientation Regulations he argued that unlike regulations that protect a religion or a minority ethic group, the new rules seemed to be designed to protect sodomy.

He rejected the comparison between discrimination against an ethnic minority and discrimination on the grounds of sexuality, saying: “I have to point out that “black” is about being. Sexual orientation is also about being. We would not wish to discriminate against people for being black or on grounds of their sexual orientation.

“The concerns being expressed this evening are primarily about sodomy rather than about sexual orientation-that is, doing not being.

“Is it not possible for such a person to hold the view that it is wrong for the state to compel him to refrain from arguing that sodomy is a social ill or to conscript him or his children into aiding and abetting it – if that is the right expression?”

In a letter to the Daily Telegraph in 1998 about Peter Mandelson’s sexuality being revealed, Lord Tebbit wrote: “In a world where Freemasons are being asked to identify themselves as such in order that the public may judge if they are improperly doing one another favours, surely it is important that homosexuals in a position to do each other favours should similarly be outed?”