Conservative leader David Cameron should "unveil the party's soul" rather than make "vacuous" reforms, ex-deputy leader Michael Ancram has warned.
David Cameron has faced growing calls to return to "core" Tory values
He told the Daily Telegraph the party should stop "trashing" its Thatcherite past and focus on issues such as lower taxes and other "core values".
Mr Ancram also said the UK could not stay in a European Union with an "agenda of ever-closer union".
The comments come after Mr Cameron said there would be no "lurch to the right".
They also emerge on the day the party's Public Services Improvement Policy Group unveiled a number of proposals, including giving council tenants state aid to help them buy a home and break up "ghettos".
Mr Ancram has written his own 30-page blueprint for the party called Still A Conservative, in which he says there is a public perception of the party "lacking an overall sense of vision and direction".
He praises Mr Cameron's "laudable efforts" as leader, saying he has "revived interest in the Conservative Party brand".
But he says: "Now he must begin to unveil the party's soul based on those core values, principles and beliefs that form the timeless make-up of that Conservative soul."
He says he supports Mr Cameron's proposal to offer tax incentives to marriage, but claims the policy of treating same-sex civil partnerships in the same way as marriages "insults the intelligence of the British people".
Mr Ancram, MP for Devizes, says the Tories must not claim to be "the heirs of Blair".
"Of course as Conservatives we must show we have changed, but we must beware doing so by trashing our past or appearing ashamed of our history," he says.
And he adds: "Change for change's sake is a vacuous process, swiftly seen through by the electorate."
Mr Ancram says his party should do more to protect "those areas of sovereignty such as fishing and trade" which have not yet been "surrendered" to the EU.
"One thing is clear. We cannot remain part of a Europe where the agenda of ever-closer union remains active," he says.
However, former health secretary Stephen Dorrell, whose Public Services Improvement Policy Group outlined proposals on health, housing and education on Tuesday, commented: "The only way we can win is if the party reaches outside its comfort zone.
"The most successful periods in the Conservative party have been when it has been on the centre ground."
He added that the group's proposed policies on social housing were a "very precise" building on Thatcher's successful right to buy policy.
Mr Cameron has in recent weeks concentrated more on so-called "core" Tory issues such as demanding a referendum on the EU treaty and saying last week that the level of immigration to the UK has been too high.
Labour has accused the party of "lurching to the right" - something denied by Mr Cameron, who has pledged to fight on the centre ground.
And there was encouragement for Mr Cameron from a Populus opinion poll* for the Times which suggests the Conservatives have risen three points on a month earlier to 36%, just behind Labour, down two on 37%, with the Lib Dems also up three at 18%.
Former party chairman Mr Ancram stood unsuccessfully as a candidate of the right in the 2001 leadership election to find a successor to William Hague. He went on to serve as deputy leader to Iain Duncan Smith and Michael Howard.
He stepped down from the front bench following Mr Cameron's election as leader in 2005.
* Populus interviewed 1,506 adults by telephone between 31 August and 2 September.