Malcolm Bruce said statistics showing a "holy grail of low inflation and sustainable growth" masked fundamental problems in the economy.

He insisted the chancellor could not evade responsibility for high interest rates just because the Bank of England had taken the decision to raise them.

"In its remit to hit the inflation target and with its only instrument interest rates, the bank has to take the chancellor's fiscal stance as given," he said.

"A more fiscally-balanced budget could have helped bear down on inflation at lower rates of interest.

"Sorry, Gordon, you are to blame, after all."

Lib Dems are threatening to vote against the next Budget

Mr Bruce also accused the chancellor of having made things "far worse" for Britain's public services, causing NHS waiting lists to rise and the percentage of GDP spend on education to fall.

"He not only stuck to Tory spending plans that Ken Clarke [the former Conservative chancellor] told me were for the birds - he made things worse by revising his inflation forecast upwards and creating a £5bn black hole that he never filed."

Mr Bruce said tax cuts brought forward by the chancellor had been paid for by rises in other areas. He promised Lib Dems would expose such "sleights of hand".

He told party delegates: "When you receive your 1p income tax reduction, count the cost of the 6% a litre petrol tax escalator - not a green tax as the chancellor claims - just another tax."

The Lib Dem spokesman urged Mr Brown to use his "war chest" for extra spending on public services and warned his party would oppose the next Budget unless this occurred.

"If Gordon Brown puts income tax cuts ahead of cutting NHS waiting times, class sizes and the needs of colleges and universities, Liberal Democrats will vote against the next Budget."

Only extra cash could get key public services such as health and education delivering acceptably, he argued.