A leading Tory MP, Michael Ancram, has launched a withering attack on civil unions, saying treating them in the same way as marriage “insults the intelligence of the British people.”

In an open attack on Conservative leader David Cameron, the MP for Devizes unveiled an alternative manifesto today calling on the party to adopt more traditional Tory policies.

Warning the leadership to stop “trashing” its Thatcherite past, he said Cameron should “unveil the party’s soul based on those core values, principles and beliefs that form the timeless make-up of that Conservative soul.”

Mr Ancram supported Mr Cameron’s attempt to offer tax incentives for marriage, but warned the leader not to treat civil partnerships in the same way.

While he accepted other long-term relationships outside of marriage should be respected for their level of commitment, he castigated the party leadership for treating them equally.

“They are not the equivalent of marriage,” he said.

“Giving them that equivalence does not enhance them; instead it diminishes the value of real marriage. In doing so it damages the concept of family and eventually of community.”

The comments are likely to bring David Cameron’s somewhat mixed record on gay rights into the spotlight.

When Labour first mentioned repealing the Section 28 amendment- which banned the promotion of homosexuality in schools – Mr Cameron said Mr Blair was obsessed with a fringe agenda, “including deeply unpopular moves like repealing Section 28 and allowing the promotion of homosexuality in schools”.

But later, in a bid to make the Conservative party appear more modern, he told the BBC: “At the end of the day, one section of our community did feel discriminated against by Section 28, and so I’m glad on that basis that it’s gone.”

Now Mr Cameron is now facing increasingly vocal calls from his party’s traditionalists to adopt more old-fashioned rhetoric.

The comments could not come at a worse time for the Tory leader.

Opposition parties and the media have begin piling the pressure on the old Etonian as a recent speeches indicate a renewed concentration on right wing issues such as crime, the EU and immigration.

Furthermore, Michael Ancram is a well-respected figure within the party. He ran for the leadership in 2001 and has served under Iain Duncan Smith and Michael Howard as deputy party leader.

In his three decades in Parliament, it is the first time he has been known to rock the boat.