They said such a haemorrhaging of talent would put even more strain on the armed forces, which are already failing to recruit and retain enough personnel at a time of growing threats.

An online petition calling for a review of the "new accommodation offer" - due to come into force next month - has already attracted more than 7,400 signatures.

It claimed that the plan "has been poorly received by a number of service personnel who will be affected".

The petition added: "If the policy is implemented as it currently stands, we believe that armed forces retention rates are likely to fall to even lower levels than those at present.

"This could have an irreversible effect on the capability of the armed forces over both the immediate and intermediate term."

The Ministry of Defence has been updating the rules on entitlement around the types of subsidised housing that is offered to personnel in the British Army, Royal Navy and Royal Air Force and - where relevant - their families.

The accommodation promise is seen as an important factor in attracting and retaining servicemen and women, though some people choose to live in their own homes.

The new offer will give ranks other than officers the ability to move into properties with more bedrooms for them and any dependents because it will be based on need rather than seniority - a move that has been widely welcomed, the defence sources said.

There will also be a fairer deal for other ranks who are single.

However, many officers will see an erosion in the kind of house they are entitled to live in following a three-year transition period.

This has caused outrage in some quarters.

One source explained why.

They said under the current system, a lieutenant colonel or a colonel - or their equivalent rank in the navy and RAF - with a partner and two children would be entitled to be allocated a four-to-five bedroom house with a floor area of 155.5 square metres.

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One rung down on the rank ladder, a major with a partner and two children would be entitled to be allocated a four bedroom house with a floor area of 137 square metres.

Under the new model, any officer of any rank is entitled to be allocated a house with one bedroom for them and then one additional bedroom per child.

This would mean the accommodation offer for a lieutenant colonel or colonel will be downgraded from a four-to-five bedroom house to a property with three bedrooms, while the major will go from a four bedroom house to one with three bedrooms, the source said.

"The minimum floor area specified in the current entitlement is removed, meaning that the officer is… entitled to a much smaller house, both in terms of number of bedrooms but also floor area," the source said.

"While not a taxable benefit, the expectation that an officer will be able to live in a larger house as they become more senior... is seen as 'part of the overall package' that we joined and remained in the army, navy or RAF for."

The source said that no compensation was being offered to make up for the loss of space.

Questions also remained about what officers and their families are meant to do with all of their belongings if forced to squeeze into a much smaller property.

The source said: "Reducing the quality of life/conditions that officers and their families live in is bound to result in many leaving the services at exactly the time that we really need people.

"The people hit hardest by the reduction in housing entitlement…are the families of majors and above - and the equivalent in the other services.

"These collectively are the most experienced people we have. They take decades of experience and vast amounts of money to 'grow' and so are the people who are most difficult to replace."

A spokesperson for the Ministry of Defence said: "Our Armed Forces personnel make extraordinary sacrifices to protect our nation, which is why our New Accommodation Offer (NAO) is built around families to modernise accommodation entitlements, making provision fairer through allocating accommodation on need, not just rank and recognising long-term relationships.

"Based on feedback from families, the NAO will also improve the standard of Single Living Accommodation, help military personnel get on the housing ladder and give our people more choice in how they live."