The Conservatives have sought to tackle claims of policy confusion following Ken Clarke's suggestion that a key inheritance tax pledge is no longer a "high priority".
The commitment to remove all but millionaires from paying inheritance tax was one of George Osborne's defining decisions as shadow chancellor.
However the shadow business secretary said on the weekend that the plans were no longer a priority, but an "aspiration" that a future Tory government would introduce when it could afford to.
The Conservative Party was forced to issue a rebuttal, saying it is a "promise we will keep", but was unable to confirm whether it would be included in the first Tory Budget.
The move is seen as being in line with Cameron's acknowledgment last week that the effects of the economic crisis would make it difficult to avoid tax rises and cuts in public spending.
Clarke later issued a statement saying: "So far as I am concerned, we are fully committed to raising the threshold for inheritance tax in the first parliament of a Conservative government, as George Osborne has promised."
Shadow Commons leader Alan Duncan confirmed to the BBC that a reduction in inheritance tax would be in the Conservative manifesto.
"We intend to ensure that only millionaires pay inheritance tax," he said.
"If we are elected, as I hope we will be, it will be in our manifesto and we will reduce inheritance tax during that Parliament."
Duncan continued: "Let's all be honest. We think that if we get into government, we are going to inherit public finances that are in the worst mess any of us have ever encountered in our lifetime.
"There are going to be some very difficult decisions to take, which is why we can't write the Budget now and George Osborne is very sensible in not doing so.
"But amongst our promises will be to reduce inheritance tax."
And Duncan claimed that the Tory policy was already paid for by moves on the taxation of the non-domiciled.
"The cost of this proposal has gone down because property prices have gone down," he added.
"The thing about inheritance tax is that it is an attack on savings. Inheritance tax is an attack on saving and that is what we need to encourage."

Dods Parliamentary Communications Ltd