The Ministry of Defence has been delivering out-of-date and inaccurate estimates of spending on operations in Iraq and Afghanistan, according to a report from MPs.

The Commons defence select committee said it was “concerned about the robustness of forecasts and estimates we are offered”.

The report provides for the first time a government estimate of how much the UK will spend in Iraq and Afghanistan in the 2008-09 financial year: £2bn ($4bn, €2.5bn), compared with £2.38bn requested last year. Of this £1.07bn is the estimate for urgent operational requirements.

The committee says more detail should be provided with these forecasts when they are provided in the future.

“No proper relation seems to exist between operational decisions, political announcements, and financial scrutiny. This simply cannot be satisfactory,” it says.

At issue is the way the ministry informs parliament of how much is spent on overseas operations. The ministry requests resources based on its main estimate for the defence budget – £34.5bn for 2008-09 – but this does not include money likely to be spent on operations. This is requested separately in two parts: a winter estimate usually issued in November and a spring estimate, issued in February with just two months of the financial year remaining.

However, the MPs say that the latest winter estimate was four months out of date when presented to parliament, and five months out of date by the time it was approved. The spring estimate was two-and-a-half months old when delivered and three-and-a-half months late when approved.

The MoD argues that it is inappropriate to ask for this money at the outset of the financial year when it does not know how much will be required.