 Operations abroad have put pressure on Britain's military forces |
In the memo, leaked to the Daily Telegraph, General Sir Richard Dannatt said the Army was undermanned because of operations in Afghanistan and Iraq.
He also said vital equipment was being used "at the edge of sustainability".
A spokesman for the Ministry of Defence said the forces were working hard but the current situation was "manageable".
General Dannatt also said the Army has "almost no capability to react to the unexpected".
He said: "It is difficult to predict the long-term effect of this level of pressure on people. It is critical that we improve manning as quickly as we can."
Revisit planning
There is reportedly just one battalion of 500 troops, called the Spearhead Lead Element, available to be used in an emergency, such as a major domestic terrorist attack or a rapid deployment overseas.
The MoD conceded that if "operations continue at this pace, we will have to revisit our planning assumptions".
Liam Fox, the shadow defence secretary, said the lack of reserves was "an appalling situation and damning indictment" of the way the government handled the Services.
"They are being asked to carry out tasks for which they are neither funded or equipped for. There is an urgent need to review our strategic approach because we cannot continue over-stretching our Forces."
In October General Dannatt said that the presence of UK armed forces in Iraq "exacerbates the security problems" and they should "get out some time soon".
He also said that initial planning for the post-war period had been poor.
