The Afghanistan crisis has shown technology cannot replace “boots on the ground”, a former military commander has said as he warned Britain’s reputation will be tarnished by further cuts to troops.

       Lt Gen Sir James Bucknall, who was deputy commander of coalition forces in Afghanistan between 2010 and 2011, urged the Government to reverse its plan to shrink the Army by thousands of soldiers.

       In a letter to The Telegraph, the retired commander said the recent Defence Review, which will see troop numbers cut to the smallest in history, had been undermined by recent events in Afghanistan.

       He wrote: “If the last few days in Afghanistan have shown anything, it is that numbers count. Strategic patience is all – you must have the critical mass to sustain an operation. The Defence Review removes that capability.

       “Technology can and must facilitate our soldiers, but it cannot replace boots on the ground.

       “After all, it was not technology that enabled the Taliban to roll up Afghanistan in a matter of weeks, a feat that came as a strategic surprise to the West.”

       It comes after Ben Wallace, the Defence Secretary, announced in March that the number of fully-trained troops able to deployed on operations will be cut to 72,500.

       The National Army Museum said the cut in troops was the lowest it has been since 1714 and the war of the Spanish Succession.

       Sir James wrote: “The context in which the Defence Review was conceived has changed. Afghanistan is a disaster of strategic proportions with implications for our foreign policy, defence policy, for Nato and for our relationship with the US.

       “If Britain wishes to retain any credibility and relevance with allies and adversaries alike, its response cannot be to cut 9,500 soldiers from the Army. The Government must revisit the Defence Review; these cuts have to be reversed.”

       The current size of the Army is 82,500, which includes around 6,000 people under training.

       The Ministry of Defence has insisted the total number of recruits in training will not be included in the reduction, meaning the size of the cut would be 3,500, not 9,500.

       Announcing the reduction in soldiers earlier in the year, Mr Wallace insisted “increased deployability and technological advantage” meant greater effect could be delivered by fewer people.

       “These changes will not require redundancies and we wish to build on the work already done on utilising our reserves to make sure the whole force is better integrated and more productive,” he added.

       Sir James’s intervention, however, follows heavy criticism from military experts and MPs across the house who have warned against cuts to conventional warfighting capabilities.

       John Healey, the shadow defence secretary, condemned the cuts to troops in March, stating that “while the threats to Britain are increasing, this is a plan for fewer troops, fewer ships, fewer planes over the next few years”.

       Tobias Ellwood, the chairman of the defence select committee, welcomed the investments in cyber and autonomous platforms, but said “they come at a huge price to our conventional defence posture with dramatic cuts to troop numbers, tanks, armoured fighting vehicles and over 100 RAF aircraft”.