In its latest assessment of its Public Service Agreement (PSA) targets set by the Government, the MoD also acknowledged that the forces were struggling to meet their designated manning levels.

Under the PSA, the MoD is supposed to be able to generate forces which can be "deployed, sustained and recovered at the scales of effort required to meet the Government's strategic objectives".

But in its Spring Performance Report, the MoD said that after the best part of a decade operating above military planning assumptions, this target could not be met.

"They (the Armed Forces) have been operating at or above the level of concurrent operations they are resourced and structured to deliver for seven of the last eight years, and for every year since 2002," it said.

"In such circumstances, the Armed Forces cannot simultaneously be ready for the full range of contingent operations provided for in planning assumptions."

While the MoD is supposed to ensure that at least 73% of units have no "serious or critical weaknesses" in their peacetime readiness levels, over the course of last year on average just 58% met the target.

In the final three months of the year, the proportion of units with no serious or critical weaknesses in the readiness levels fell to 53%, compared with 67% in the last quarter of 2006.

The MoD also warned that the forces' manning targets were likely only to be partly met. At the start of the year, according to the latest figures, the Navy was at 96.5% of its full strength - 1.5% below the "manning balance" target; the Army was at 96.4% - 1.6% below target; and the RAF was at 97.7% - 0.3% below target.

The report said that the forces were on course to achieving the PSA objective of securing success in the military tasks they undertake, although with "some risk".