Conservatives have asked parliament's spending watchdog to probe "missing" NHS cash.

The move will highlight Tory warnings that extra NHS cash is failing to make an impact on frontline services.

And Dr Liam Fox's focus on "missing NHS money" will revive Labour claims that he is aiming at health budget cuts.

The shadow health secretary is convinced that real increases in money are not being translated into treatment for patients.

He does not accept explanations from ministers that "these developments [are] the result of greater activity in the primary care sector or of an increase in out-patient treatments".

Fox questioned why NHS spending increases of over a fifth in two years have led to drop in hospital admissions and only small rises in activity.

"According to official figures, a real increase of 21.5 per cent in spending over the period 1999/00 to 2000/01 by the Department for Health translated into an increase of only 1.6 per cent in finished consultant episodes (a standard measure of hospital activity).

"Further, admissions to hospital actually fell by 0.5 per cent over the same period," he said.

In a letter to the National Audit Office the shadow health secretary requested an investigation - and accused the government of hiding the truth.

"Taxpayers legitimately ask where the money has gone," he stated.

"As ever, it is difficult to get adequate information from ministers. We therefore turn to the Audit Commission to obtain a true picture for us."