Ministers said that the increased costs reflected the need to purchase new defensive equipment to protect troops against the constantly changing insurgent threat.

But the Tories said the decision to pour in extra cash amounted to a belated recognition by ministers that for years operations in the two countries were not properly funded.

The Commons Defence Committee, which revealed the increases, expressed "surprise" that the cost of operations in Iraq was rising at a time when British troop numbers there were falling.

According to the Ministry of Defence's latest "spring estimates", spending on operations in the two theatres for the current financial year is forecast to be £3.297 billion - a 94% increase on last year's total of £1.698 billion.

The forecast for Iraq is £1.449 billion, up 52% since the last set of "winter estimates", while operations in Afghanistan are expected to cost £1.424 billion, an increase of 48% on the previous estimates.

The increases will be paid for out of the Government's reserves and will not affect the defence budget

Armed Forces Minister Bob Ainsworth said that the Government had a duty to ensure personnel in the field were properly equipped, while welfare changes, such as the payment of operational bonuses, had also pushed up costs.

But shadow defence secretary Liam Fox said: "We have been complaining for a long time that these operations are under-resourced. It appears that this is something the Government seems to belatedly recognise only now."

Overall, the MoD is forecasting that it will need an additional £2.192 billion for the current financial year over and above the previous winter estimate.