The number of trained service personnel in all three branches of the armed forces is likely to be cut by about 20 per cent over the next six years as drastic reductions in the Ministry of Defence budget are implemented, according to a new study of Britain’s military future.

As defence chiefs prepare for a big overhaul in the size and structure of military expenditure after this year’s general election, the Royal United Services Institute, a think-tank, has produced the first model of what the armed forces could look like if the next government implements expected cuts in MoD spending.

According to the study, the next government is likely to cut the MoD budget by between 10 and 15 per cent in real terms over the six years from 2010 to 2016. This is based on what the analysis calls the “cautiously optimistic” assumption that the MoD will be awarded a 0.5 per cent annual cash growth in its core budget after 2010-11.

If this proves correct, a programme of cuts that is evenly spread across all three services would see the overall number of trained service personnel fall from 175,000 in 2010 to about 142,000 in 2016.

The study calculates what an even spread of the cuts across each of the services would mean. For the army, it predicts that the number of ground formations – including infantry, armour, artillery and support regiments – would come down from 97 to 79.

The Royal Air Force would find that available aircraft – fixed wing and helicopters – fall from 715 to 615. Major vessels, including submarines, carriers, escorts and big supply ships – would fall from 57 to 46.

The institute says a reduction on this scale would be of the same order as the one Britain undertook between 1988 and 1998 when it reduced capabilities as a result of the end of the cold war.

“However, it would be significantly greater than the 4 per cent reduction between 1964 and 1970, the period when the withdrawal from east of Suez was substantially completed,” says Malcolm Chalmers, the report’s author.

Defence chiefs have long expected a big cut in spending after the next election, because neither of the two main parties has ring-fenced military expenditure in its policy priorities.

The critical issue that the next strategic defence review must decide is whether to conduct these reductions in the balanced way implied by the institute’s study. The UK could decide, for example, to rebalance strategy to favour land forces, a decision that would lead to even bigger cuts in the number of ships and aircraft, and the personnel to operate them.

The MoD is set to take an early look at the possible new strategy for the armed forces when it publishes a green paper on the issue in March. However, Mr Chalmers warns that uncertainty over the future nature of conflict means it is unlikely that the UK will forgo key capabilities altogether.

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