Surprise, surprise. A defence secretary thinks Britain should spend more on defence. The former Pentagon boss Robert Gates is in Britain promoting his old lobby and his new book. He is concerned that Britain's current defence cuts may deprive the Atlantic alliance of "full-spectrum capabilities". They will weaken the world's fourth largest armed force (Britain's, believe it or not) in deterring dreaded foes. George Osborne is supposed to shake in his shoes.

Gates is a careful man. He bears the same Washington scars as his predecessors, Robert McNamara and Donald Rumsfeld, in trying to reform a potent and reactionary defence establishment. The US fields the most awesome military force in history, yet it keeps losing wars and its global paranoia knows no bounds.

In his memoir, Gates is horrified by Barack Obama's micromanagement of America's wars. The advent of modern surveillance and drone technology means that, "for too many people … war has become a kind of video game", he says, professing himself "even more sceptical of systems analysis, computer models, game theories and doctrines that suggest that war is anything other than tragic, inefficient and uncertain".

Yet Gates retains a conservative belief in extravagant weapons systems as relevant to today's international confrontations. He approves of nuclear missiles and thinks Britain should have more. He criticises it for not having an aircraft carrier in operation, despite the two costly and purposeless ones on order. They are as much use as war horses and Welsh archers.

I occasionally attend defence seminars to immerse myself in exotic surrealism. A recent one comprised soldiers, thinktankers and arms suppliers, all living off the public purse. They were like Macbeth's witches, incanting: "By the pricking of my thumbs / Something wicked this way comes," before stirring quantities of money into their budgetary brew. "Thrice to thine and thrice to mine / And thrice again, to make up nine," they chant, the nine being billions, not millions.

No one at these events ever talks about who is being defended against whom. We are just warned that if the defence lobby does not get its money, "capabilities will degenerate" and allies desert. Assorted "wars", on terror, drugs, human traffickers or whatever will be lost and unmentionable horrors result. The Ministry of Defence is like Benefits Street for slow learners.

Without some idea of an enemy, we cannot judge how much defence is needed where. Not since the end of the cold war has there been a sensible threat to Britain. The defence lobby has cleverly converted criminal deeds by terrorists into threats to "national security". This is lobbying talk, not reality. The truth is that, other than the eccentric Falklands engagement and the domestic policing of Northern Ireland, every war to which British troops have been committed has been an aggression against a foreign state, aggression to which we currently devote some £40bn a year.

Gates maintains that today's threats are as dangerous as during the cold war, coming from the Middle East and Asia generally. I know of no states that pose even the remotest threat to the UK or Europe as a whole, let alone one that would be deterred by armies, navies and air forces or by nuclear missiles. If massive deterrence worked, there would have been no Falklands invasion or 9/11 attack.

A few hot-headed terrorists may threaten dire deeds, but rarely more than bomb blasts. These are matters for the police and security services, whom God preserve. They have nothing to do with military deterrence. Indeed, as most are suicide attacks, they are plainly immune to deterrence.

The truth is that British defence activity over the past quarter century has not been defensive at all, but interventionist and aggressive. It has taken the form of attacks on Serbia, Afghanistan, Iraq and Libya. These wars may have admirable motives, in some cases humanitarian, but they are wars of choice.

Such wars are thankfully drawing to a close as people weary of them and their inability to spread peace or stability, or even humanitarian relief. The debacles of Afghanistan and Iraq showed powerful states seeking to impose their will on weak ones, leading the weak to become mysteriously stronger.

Nato in Afghanistan, with Britain in a lead role, was a mercenary army dragooned by the US into helping avenge the security lapse of 9/11. It was a war of choice that has killed tens of thousands of people, while not increasing Britain's security one jot. It was more a 19th-century gesture, fought for little other reason than to show the muscle of western military might when Nato had little else to do.

Britain's defences have no need for lumbering aircraft carriers and destroyers, for fighters and bombers, drones and tanks. As the new chief of the defence staff, Sir Nicholas Houghton, recently remarked, British policy is heading towards "a strategically incoherent force structure: exquisite equipment, but insufficient resources to man that equipment or train on it". This "hollowed-out force" dances to the tune of the defence contractors, in whose hands Osborne and David Cameron are putty.

The reality is that the devil makes work for idle military hands when there is no conceivable risk of attack. The drone wars that the US and Britain are now waging across the Muslim world have become testing grounds for the makers of these dreadful weapons. Armed forces sit champing at the bit. Defence industries gasp for money. Belligerents demand that "something be done" in Syria or wherever.

Perhaps Ministry of Defence has become a misnomer. It should be renamed the Ministry of Attack.