The former Chief of the Defence Staff Lord Stirrup has told MPs that there needs to be better "discipline" in the ambitions of the armed forces.
He said that the Ministry of Defence had sometimes tried to do too much on limited resources.
Speaking to the Defence Committee on 18 May 2011 as part of an inquiry into the Strategic Defence and Security Review, he said "the amount of national wealth given to defence is a political decision, but then you must restrict your ambitions to what is available".
The review was announced by the prime minister in October 2010, and included an 8% cut in defence spending in real terms over four years.
Mr Cameron said that RAF and Navy numbers would be reduced by 5,000 each, Army numbers by 7,000 and the Ministry of Defence would lose 25,000 civilian staff by 2015.
Asked by Labour MP Sandra Osborne what areas of the review could be revisited, Lord Stirrup said simply "money".
The committee also heard from Sir Rupert Smith, a former General Officer commanding the British Army in Northern Ireland.
He told MPs it was time to stop treating defence and security issues as "parallel but separate activities".