Michael Howard today held out the prospect of further tax cuts beyond the £4 billion he offered yesterday.

The Conservative leader has come under fire from some in his party who believe the cut - worth less than £200 a year to each household in the UK - is not ambitious enough to grab voters’ imagination.

But he stressed today that the £4 billion cut related only to the first Budget of a Tory administration, and said that further reductions may follow in subsequent years.

In an interview on BBC Radio 2’s Jeremy Vine programme, Mr Howard insisted he would be "responsible" in his election campaign promises.

Most of the £35 billion savings from "wasteful" Government expenditure which the Conservatives have identified - some £23 billion - would go to improving frontline services, while £8 billion would be used to reduce the national debt. Only the remaining £4 billion would be used to cut taxes, mostly for the benefit of lower-paid workers, first-time buyers and small businesses.

But the Tory promise was "a great deal better" than the tax increases which Labour would impose if it won, said Mr Howard

He added: "Of course I would like to do more, and I hope that over a period of time we will be able to do more.

"But I am also absolutely determined not to make any promises I can’t keep.

"We are talking here about our first Budget after the election.

"We are making a firm promise that in that first Budget we will cut taxes by £4 billion.

"Later, I hope to do more, but because I know I can’t make firm promises that that will happen after that first Budget, I am limiting what I say to the promises I know I can keep."

Mr Howard and his Shadow Chancellor, Oliver Letwin, are due to flesh out their proposals within the next few weeks. They are likely to promise that tax thresholds would be raised to take more people out of income tax, and stamp duty would be cut or eliminated for people joining the property ladder.

The extra £23 billion for public services would be spent on Tory priorities such as cleaning hospitals, improving school discipline and recruiting an extra 40,000 police.

Labour yesterday accused the Tories of double-counting ,by including the £21.5 billion of cuts by 2008 identified in their own review by Sir Peter Gershon. The Conservatives replied that they were not claiming that the whole £35 billion was in addition to Gershon but that they had accepted most of his plans.

Mr Letwin admitted to The Times yesterday that the sum earmarked for tax cuts was "modest" and said: "But I would say that if there is a black hole in the public finances, you have to take action over that first. You cannot just ignore it."

He said that he and Mr Howard had concluded that "we should be very safe and hold back £8 billion for the purpose of reducing borrowing".

Mr Howard announced the outcome of a year-long review of government spending carried out for the Conservatives by David James, the business troubleshooter. The Tory leader, brushing aside the defection of Robert Jackson to Labour, said that there was a clear choice at the next election: more waste and higher taxes under Tony Blair or value for money and lower taxes under the Conservatives.

In a pre-emptive news conference called to rebutt the Tory plans before they had even been announced, Alistair Darling, the Transport Secretary, said that the claimed savings fell apart under scrutiny. Giving an example, he said that the Tories proposed savings from privatising the driving test, which he said was already "outsourced".

However, the Conservatives replied that the driving theory test is a very small part of the Driver Vehicle Operating agencies, which they would privatise wholesale.

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