The Budget was a missed opportunity that will hit British business, Iain Duncan Smith has said.

In a speech to the British Chambers of Commerce on Monday the Conservative leader renewed his attack on Gordon Brown's decision to raise taxes to pay for the NHS.

"Our share of world exports continues to fall. Our productivity growth, which used to be faster than that of the United States, has been slower of the past five years," he said.

"What was different about last week was simply that Gordon Brown decided to break cover. The end result was still same - business got clobbered.

"Increasing National Insurance Contributions is a straightforward tax on the income of workers and an outright tax on jobs for the firms who employ them. More than that it is a cowardly and insidious way to put up income tax."

As part of the Conservative response to the Budget, the speech also hammered home the party's view that the money raised for the NHS will only serve to increase the wages bill for the NHS and result in limited improvement because of inefficiency.

"Ministers talk about the extra resources they will put into the NHS. The extra doctors, nurses, GP centres and hospitals we will have. This is the same thing they've been saying for the last five years," he said.

"In reality this government has already increased NHS spending by nearly a third in real terms. But the quality of the service the public actually receives has deteriorated."