The invasion of Iraq was a mistake. It was wrong to say that Saddam Hussein had weapons of mass destruction. Tony Blair was selective about the intelligence reports, preferring those that told him what he already believed. These things may seem self-evident, four years into a violent and chaotic war, but coming from Lord Guthrie they have an impact approaching shock and awe.
"I felt it was right at the time," the former head of the armed forces says of the decision to attack Saddam to stop him attacking us. "Now I'm not so sure. In fact I think it was probably wrong."
The occupation has been a disaster, he says. But this is the man widely credited – or blamed – for encouraging fresh-faced new PM Tony Blair to become a hawk willing to send British troops to die in Kosovo, Afghanistan and Iraq. As Chief of the Defence Staff from 1997 to 2001, Charles Guthrie struck up a close relationship with the then Prime Minister and became known as Mr Blair's favourite general. Even after retirement he was close to the PM, acting as his envoy to Pakistan. So what is he up to now, publicly admitting doubts and regrets in a way that would have been impossible back then?
The old boss is gone, of course. He can speak frankly because there is no more need for loyalty to No 10. Quite the opposite: Lord Guthrie blames Gordon Brown for what he sees as the distressing state of the armed forces. They are underfunded and "very, very stretched" by fighting two wars, he says. They need more money, urgently. "Lives will be lost if we go on doing what we're doing."
That is already happening. On this Remembrance Day The Independent on Sunday identifies more than 80 cases in which service personnel have died due to shortages, failures or mistakes caused by overstretch. Even as this interview takes place in the City of London, the inquest into the death of Fusilier Gordon Gentle is finishing in Oxford. The death of the 19-year-old in Basra in 2004 was due to "chaos" in the Army's supply chain, according to the coroner. His vehicle was not fitted with a device that could have saved him. Lord Guthrie says some parts of the armed services are "marvellously equipped", but in others the strain on the system is causing mistakes that can lead to death. "Undoubtedly," he says, "that will happen more and more."
Lord Guthrie is clear that the services are in this state largely because of the man who was Chancellor for a decade. "I certainly viewed Brown as unsympathetic to defence," says the retired soldier tersely. "He didn't make much effort to educate himself about defence." Is he saying that the spending he thought vital was approved of by the PM but blocked by the Chancellor? "That is exactly right."
Wasn't the time to say this when he was in power? "I did," insists Lord Guthrie, who recalls "huge rows". And he reveals, for example, that feelings ran so high he came close to resigning during the Strategic Defence Review of 1998. That would have been a huge blow for Mr Blair.
"We had taken the Treasury by the hand through it all and thought we were home and dry," he says. "Then at the last moment Brown tried to take a lot more money out of it. If he had, the whole thing would have unravelled."
How close did he come to resigning, exactly? "Couple of hours, I suppose." And how was he persuaded not to do it? "I didn't get as much money as I wanted, but I got enough to stop me resigning."
Lord Guthrie, a white-haired 68-year-old in a navy blue suit, is in a meeting room at the City financier NM Rothschild, which employs him as a non-executive director. Pale and seeming slightly weary, he speaks with a slight lisp, and rarely raises his voice. But he is also Colonel Commandant of both the Life Guards and the Special Air Service, honours that can only be earned by being tougher than a rhino wearing body armour.
He knows the power of understatement, when he says of Mr Brown: "I hope that he understands better now than he did then." The new Prime Minister has visited troops in Afghanistan and Iraq. "I hope that, because he has seen more and realises what they're up against, he will now be more sympathetic."
Lord Guthrie is a patron of the new UK National Defence Association, a group of former military leaders who want defence spending raised to 3 per cent of GDP, or £44bn a year. That is £10bn more than now.
The association wants to create a mass movement that will demand we treat our soldiers, sailors and airmen properly – but one already exists. The IoS is one of those calling for the repair of the Military Covenant, the debt of care owed to those who serve. The British Legion has also mobilised huge support.
"When you become a soldier, a sailor or an airman you do take tremendous risks," Lord Guthrie says. "You have to make personal sacrifices, perhaps a supreme sacrifice. The Military Covenant says that if you are willing to do that, really, it's up to the Government to look after your interests, your family, make sure they're housed properly, make sure you're equipped properly and not taken for granted."
Every government insists the security of the nation is a priority, he says. "Well, you've got to do a bit more than talk about it. A lot of servicemen feel they're rather taken for granted while being asked to do really terrible, dangerous things which other people don't want to do."
Underfunding started with the Conservatives but has never been addressed seriously by Labour, he says. "As a result you have houses for families to live in which are slums." Soldiers will leave in even greater numbers if nothing is done, he says. "The Army is too small for what it's being asked to do. Eventually, and we've already seen signs of this, they won't want to stay."
General Charles Guthrie, Baron Guthrie of Craigiebank, was in the Army all his adult life. Born in November 1938, he was educated at Harrow before Sandhurst. His active service was divided between the Guards and the SAS, including tours of duty in the Gulf, East Africa and Northern Ireland. Married with two grown-up sons, he is now on the boards of several firms, including that of the arms manufacturer Colt Defense LLC.
He has also just written a book called Just War with the defence expert (and fellow Catholic) Sir Michael Quinlan. Mainly exploring that Christian tradition, it sets out the tests historically used to decide whether war was just. "They battled with questions in exactly the same way as we do," he says. "You have to think, are you going to make things worse? What is your plan to put things right after war? There are certain things you don't do in war, like kill women and children."
Afghanistan passed the old tests, he insists. "They were training people to kill us and to kill the Americans. Attacking the training camps was just." But what about Iraq? He has a problem with that question. "I'm Colonel [Commandant] of the SAS and the Life Guards. They're both in Iraq. For the Colonel to be saying he thinks the whole thing is a great mistake is not a good idea."
But while the invasion was brilliant, militarily, he says, the occupation was catastrophic. "Disbanding the Iraqi army was crazy. We should have taken them to our bosom and said, 'This is your country, we're going to help you rebuild it.' There was no real plan."
Was there just cause? Lord Guthrie, still close to Tony Blair, told the House of Lords in 2002 that Saddam posed "a serious threat" that would endanger "the security of our own citizens". That wasn't true, was it? "It's very easy to be wise after the event but everybody – the Americans the British, even the French – believed he had weapons of mass destruction."
Not everybody. Not the million or so people who marched through the streets of London. "He behaved as though he had weapons of mass destruction," insists Lord Guthrie. "Now whether that was a good enough reason to try to remove him, I don't know."
He believed Saddam had nuclear weapons and action was needed to prevent an attack. "What I was told, and all the intelligence agencies were saying, was exactly what I have just said. I felt it was right at the time. Now I'm not so sure. In fact I think it was probably wrong."
That is quite an admission. There is, he acknowledges, a big problem with the sheer size of those intelligence reports. "You tend to select – maybe this is human frailty – the intelligence which rather supports what you want to do." But who exactly was selective in this case? "I think the Cabinet. I think the overseas policy committee. I think the Prime Minister."
How close was he to Mr Blair? "We used to talk about things," he says, almost tenderly. "I could say anything to him, because he knew I wasn't going to spill the beans." Astonishingly, the subjects discussed included invading Zimbabwe, "which people were always trying to get me to look at. My advice was, 'Hold hard, you'll make it worse.'"
Did these two Christians ever discuss their shared faith? "No," says Lord Guthrie, rattled. "Never talked to him about it." That seems extraordinary. "I never ever talked to him about it." OK. Moving on... "I really have never talked to him about it."
Right. There may be a reason why Lord Guthrie is cagey about faith. He is vice president of the Sovereign Order of Malta, a humanitarian organisation with an image problem, having been founded in Jerusalem in 1050. The order says it "had to become military to protect the pilgrims and the sick and to defend the Christian territories in the Holy Land". That stopped 200 years ago, but it still requires those who become knights – by invitation only – to swear to defend the faith. So he's a knight in the order. And he's written a book about just war. And he was head of the armed forces. How does he think that sounds to Muslims who accuse Britain of being drawn into a new crusade?
"Well," says Lord Guthrie, "I... I suppose you could interpret it that way. I've never noticed it or... I've never really thought about it, really." He thinks for a moment. "I've never discussed having more crusades, or anything like that."
That is, perhaps, a joke. Or at least a way of shrugging off the awkward question. Military commanders are never at ease with those, even in retirement. But Lord Guthrie rises to leave with the air of someone who knows himself unchallengeable. He has said his piece. Gordon Brown has been given his orders: pay up, if you want the boys to go on fighting. As far as the general is concerned, that is really all that matters.
Further reading: 'Just War' by Charles Guthrie and Michael Quinlan is published by Bloomsbury, price £10