Ministers have been urged to study the criticisms by a senior army commander, who resigned over the campaign in Afghanistan.

Major-General Andrew Mackay, the head of the Armed Forces in Scotland, Northern Ireland and northern England, is felt there was a lack of support for troops in Afghanistan, where he was in charge of 8,000 troops during a six-month tour that ended last year. He is also said to have concerns about plans to restructure senior levels of the Army.

General Mackay, 52, who resigned his post on Thursday, just three months into his three-year role, was commander of the Helmand Task Force from October 2007 until April 2008. He was said to have been taken aback to discover senior officers “making it up as we go along”.

He also sent a memo to London that warned of a “grave crisis” over equipment that was “tired, limited and failing regularly”. In November he admitted in an interview with The Times that the Army was failing to eradicate the problem of poppy production.

Although the MoD insisted that he had left for “personal reasons”, others close to the Army chief suggested he was frustrated with the Government’s approach to the war in Afghanistan.

Major Nick Haston, who had been General Mackay’s deputy chief of staff before he himself resigned from the Army in protest at policy and equipment shortages, said: “I’d be assuming that frustration ... in Afghanistan would be part of the issue.” He added: “There will be another round of restructuring, I’ve no doubt about that, and he might have been exposed to this. So that would also have contributed to this decision.”

He described the general’s resignation as “a serious blow”. Major Haston said: “He has an intimate knowledge of the approach that needs to be taken in Afghanistan.”

Asked why the army chief had quit, Clive Fairweather, a former commanding officer of the King’s Own Scottish Borderers and a close friend of General Mackay, said: “I think there are three reasons. The first one — and he is not the only commanding officer to feel this way — is frustration that the country is at war in Afghanistan but the Government is not on a war footing. When the Falklands was on, with similar numbers of troops involved, there was a Cobra [emergency committee] meeting on every day with senior ministers. Now all we have is Bob Ainsworth [the Defence Secretary].

“The second is that the Army are going to be scrapping his command anyway, and nobody will be running anything in Scotland. And third, he is probably at an age where he wants to do other things.”

Mr Fairweather added that General Mackay had a “very, very strong conscience”.

Trevor Royle, a defence analyst, suggested that General Mackay was “a principled soldier” who was standing by his beliefs. “He believed very strongly that there were shortcomings in equipment levels in Afghanistan ... and having made his decision on that point he clearly felt that he had to resign from the Army,” he said.

General Mackay is the fifth senior officer to leave his post prematurely in the past two years and the highest-ranking since operations in Afghanistan began.

Eric Joyce, the Labour MP who this month resigned from his post as parliamentary aide to Mr Ainsworth, urged the Government to heed General Mackay’s concerns. Mr Joyce, a former Army major, said: “He is a very high-grade young general and I can’t remember a precedent of a 52-year-old giving up. Everything he says must be looked at carefully because he is a very credible guy.”

Angus Robertson, leader of the Scottish Nationalists, at Westminster said that General Mackay’s departure “underlines the serious dissatisfaction within the military over the UK Government’s strategy in Afghanistan, and the support provided for our forces”.

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