On Saturday, the day after the British parliament voted to enter a third war in Iraq, his breakfast was undisturbed. Last year he retired after 42 years of service, becoming General Lord Richards. The man who had been involved in every conflict from Cold War Germany through Northern Ireland, East Timor, ­Iraq, Afghanistan and Libya is in the unaccustomed position of watching from the sidelines.

That is not to say he does not have an opinion. Loved by journalists for being Britain’s most outspoken general, when he seemed to contradict government policy on Libya he was rebuked by Prime Minister David Cameron: “You do the fighting, I’ll do the talking.”

When I ask him if he wishes he were still involved, he says, “Not really. I have great confidence in (US military chief) Marty Dempsey and Nick Houghton (his successor as chief of defence staff) and I know Cameron is up for a proper debate.”

But that does not mean he agrees with the Prime Minister’s plan for dealing with ISIS, as he refers to the Islamic State. “If you have been involved with as many wars as I have, the first thing you learn is that you don’t do wars unless you really have to.

“Politicians have a tendency to think you can sort things out militarily. I’ve always been leery of going to war. Secondly, if I’ve learned anything in 42 years’ military experience, much of it in command, it’s that you don’t do it if you’re not going to do it properly.”

That, in his view, means if you really want to defeat the Islamic State, you must be prepared to put your own boots on the ground and not restrict yourself to Iraq.

“You can’t possibly defeat ISIS by only attacking them in Iraq,” he says. “How the hell can you win the war when most of your enemy can end up in a country you can’t get involved in?

“Even if you are successful in Iraq, which I doubt, they will just go into Syria, and what will you have achieved? They will just have tighter lines of communication.”

He worries that politicians are “misunderstanding the situation in Iraq and Syria” by framing it as a counter-terrorism issue.

“ISIS is not a terrorist organisation. It might commit acts of terror but it has tanks, artillery, huge wealth, courts, justice of its own kind, and is administering large areas, so the idea that this can be seen as a counter-terrorism campaign is a key error.

“We have to view it as a conventional campaign, which means you have to have boots on the ground. This doesn’t mean they have to be Western, but you do have to have an army to contain, defeat and destroy. You can’t do it by air alone. History cannot be rewritten. There’s never been a campaign where that has happened.”

Richards questions whether Western countries can sustain what is likely to be a long and demanding air campaign.

“This is not drone attacks in western Pakistan or the odd bomb over Somalia, it’s a sustained air campaign to write down the combat power of ISIS ... These air systems are very expensive and our air force is small because we’ve all been cut. I’m not sure how long we can sustain this.”

There is an element of “I told you so” in this. Two years ago he presented a plan to the British government to train a 120,000-strong rebel Syrian force to fight President Bashar al-Assad’s military. He believes it would have prev­ented the emergence of the Islamic State. “I won’t over-egg it,” he says, “it was just a plan.” But he argues the government’s obsession with getting rid of Assad, rather than training rebels, ultimately may have caused more deaths.

“By giving sufficient help, together with the Americans and French and so on, to keep the war going, but not sufficient to allow opposition groups to win, what we did was allow the fighting to go on rather than conclude.

“From the frustration of those good opposition groups has grown a bigger problem today — ISIS — and that’s what we’re now having to manage. We could have pre-empted all this by dealing with Assad in the coherent way that those groups were asking us to do in 2011-12.”

No one could accuse Richards of modesty: when he served in Afghan­istan his staff would say, “the ego has landed” if he was on his way. His autobiography, Taking Command, is published this week and is full of mentions of how, if people had done what he suggested in Iraq/Afghanistan/Libya/Syria, we would never have got into our present situation.

Were he still the chief of defence staff, what plans would he draw up to defeat the Islamic State? “There are two ways,” he says. “Either a Western army or a revamped version of my plan against Assad. The key question is who do you use? The (Kurdish) Peshmerga and Iraqi forces should be the basis, then other Arab armies have to decide if they want to deal with this regional force that threatens them all.

“The Gulf states, Egypt — many of them spend billions on defence but are not accustomed to deploying forces to other places. This would take at least a year and need mentoring and specialist help from Western forces. You’d also need Turkey being robust about its borders and some unspoken arrangement with Assad. The only way to do it effectively is to use Western armies.”

Can we destroy the Islamic State? “I don’t think so, but we can defeat it,” he replies. Even if the British government were to deploy troops in training and mentoring — which would mean some being deployed in combat — that would not be enough. “If you’re not going to fight full-bloodedly, you’re ceding to the enemy.”

He warns: “They are not going to just sit there and soak it up. We should expect ISIS to plan counter-attacks, either asymmetrical or symmetrical, to really spoil the day of whoever is attacking them.”

What he would like to see is a serious international response along the lines of that which led to the creation of NATO at the start of the Cold War.

“(Islamic State) is to me the biggest threat facing our way of life, and we’ve woken up belatedly to it. The scale of the problem needs a scale of response and vision our leaders are unaccustomed to. I would compare the requirement to that of their forebears in 1947-48 in response to the Soviet threat.”

Richards points out that the scale of the challenge is massive. “It’s no good just dealing with ISIS. Our strategy has to encompass support for Nigeria (where Boko Haram has declared its own caliphate in the northeast), shoring up Kenya’s fragile position, and more needs to be done in Som­alia. You have al-Qa’ida talking of spreading to Myanmar, Pakistan is very vulnerable ... Afghanistan must be seen through to make sure (it) doesn’t become part of the caliphate early on.

“I see all the foundations for (tackling) that but haven’t heard it talked of with ‘proper strategy’. There’s bits of this and that, and countries coming together, but they haven’t really understood that if you just press here, it will rise up there.”

Some argue this is the Arab world playing out the 1300-year-old schism between Sunnis and Shi’ites and nothing to do with us, so I ask: is it really our fight?

“If I was still CDS and doing the strategic estimates, one would be: should we be getting involved in this epoch-making change of boundaries in the Arab world? On balance I’d say yes, as for our allies in the region the genie is already out of the bottle — it’s too horrible to contemplate.”

Richards sees no contradiction in doing a deal with Assad.

“These wars go on perennially, and thousands die,” he says. “Is it moral not to seek a political outcome with a man who might be many people’s idea of the devil? When there can be a political outcome, the bigger devil is war. I am disappointed to hear that possibility discounted; it means that if Assad chooses to, he can frustrate our attempts to deal with ISIS, and that is barmy.”

For the same reason he believes we must come to a quick arrangement with Russia over Ukraine, and accept the annexation of Crimea. “I don’t want to sound (like) an apologist for Russia, but think Falklands, think Cuba, and you begin to understand what Russia feels about Ukraine,” he says. “It’s been a part of their country for hundreds of years.

“Crimea is Russian. The Russians, British and French went to war over Crimea 170 years ago. The idea that Crimea was ever going to be allowed by Russians to be part of Ukraine, or a Ukraine that was hostile, was cloud-cuckoo-land. And from a purely military sense it was a rather cleverly executed plan.

“Rather than us getting back into some sort of Cold War, I want to see Russia brought into the family of nations ASAP because the bigger threat to us all is these non-state extremists.”

He asks: “When you go back to what happened in Kiev, are we ­really certain those protesters in the early days were properly representative of the majority of Ukraine? There were certainly some dodgy elements, and a president who was democratically elected was kicked out, however much you don’t like him.

“When the coup happened, we instinctively supported the oppressed against the autocrat. I am not saying that’s wrong, but did we properly analyse the situation before we gave them moral support that we could never follow through in a physical sense?

“What worries me is we keep encouraging people to get to the top of the hill but can never fully support them in the way some would want.”

In the same way he queries whether we should have been so enthusiastic about the Arab spring.

“We have this natural, liberal, Western instinct to encourage those who want our kind of democracy.

“The question has to be: are these countries yet able to manage the pressure and responsibility, given that they are so riven by ethnic, religious and tribal divides that any democracy on any scale is very difficult to deliver practically? The types of representative government the Middle East has enjoyed for hundreds of years may still be the best for them now, and maybe we should be a little less convinced that ours is automatically the right one for everyone.”

He adds: “I know I’m treading on delicate toes, but if you are an average Syrian or Libyan or Egyptian, this experiment in Western-style representative democracy has not been very good.

“If those people had known back in 2011 that what they were asking for would lead to the situation today, I doubt any of them would have asked for it.

“We need to think very carefully what we are doing even now, going into Syria and Iraq, and make sure that what we’re suggesting will actually lead to a better life for the average person.

“In the case of Syria, the role of minorities in the country — the Alawites, Maronites, Druze and wealthy Sunni businessmen — has actually been very stabilising. We are at risk of destroying that, and of it leading to complete anarchy and the breakup of Syria. I’m not sure we’ve thought it through.

“We, in the military, have a doctrine for everything, and one of the key requirements is to understand the environment into which one is going,” he says.

“I remember in 2011 very senior people in Whitehall telling me there were no tribal issues involved in Libya. I said, ‘Hang on, I’m no Libya expert but I can tell you, it’s huge.’ But they resisted; now look.”

THE SUNDAY TIMES