Gordon Brown was malign and Tony Blair lacked moral courage, says General Dannatt

The former head of the Army, General Sir Richard Dannatt, has described Gordon Brown as "malign" and attacked Tony Blair as lacking in "moral courage" for failing to support the armed forces.

The General also declared that evidence for Iraq's possession of weapons of mass destruction – the official justification for Britain joining the US-led invasion – was "most uncompelling" and the planning for the aftermath of war an "abject failure".

The former commander became outspoken in his criticism of the government while he was in his post, a stance which many felt cost him a possible promotion to the head of the military. But his decision to join the Conservative Party as an adviser soon after retiring was condemned by some of his senior colleagues.

Yesterday General Dannat appeared to question Chancellor George Osborne's insistence that the estimated £20bn cost of renewing Trident must come from Ministry of Defence budgets, rather than being paid for by the Treasury. Warning that the "huge" cost of Trident will come on top of cuts to the MoD budget totalling as much as £35bn over the next few years, General Dannatt said: "I don't know whether the full implications have really been understood."

The General's most scathing criticism was reserved for the two former prime ministers, over the way the forces were funded in Iraq and Afghanistan. Writing in his memoirs, he said: "In my view Gordon Brown's malign intervention, when Chancellor ... by refusing to fund what his own government had agreed, fatally flawed the entire process from the outset. The seeds were sown for some of the impossible operational pressures to come."

Mr Blair "lacked the moral courage to impose his will on his own Chancellor," the General wrote. "Every organisation has its tone set by its leadership. To me it seems extraordinary that the Prime Minister, the No 1 guy, cannot crack the whip sufficiently to his very close friend, the Chancellor, and say 'We're doing this in the national interest, Gordon, you fund it'."

In his book, serialised in The Sunday Telegraph, General Dannatt complains that after Mr Brown became Prime Minister in 2007, he did not have regular enough opportunities to talk with him about the problems the Army was facing to the extent that in early 2009, he was forced to "ambush" Mr Brown during a chance encounter in Horse Guards Parade to get across his concerns about Afghanistan, where British troops were suffering high casualty rates.

All five candidates for the Labour leadership condemned the General. Ed Miliband said: "The language of betrayal is frankly reprehensible." David Miliband said the comments would be painful to those who have lost relatives in the wars. "To be told it could all have been easier and better if it hadn't been for some bureaucrats and politicians – it's just not true." Ed Balls and Diane Abbott both criticised General Dannatt for becoming a Tory adviser. Andy Burnham described the General's criticisms as "misplaced", saying that he had seen both Mr Blair and Mr Brown "agonising" over the decisions they made.

The MoD said yesterday that a British soldier from The Royal Scots Borderers was killed by a rocket propelled grenade in Helmand.