I say cut defence. I don't mean nibble at it or slice it. I mean cut it, all £45bn of it. George Osborne yesterday asked the nation "for once in a generation" to think the unthinkable, to offer not just percentage cuts but "whether government needs to provide certain public services at all".

What do we really get from the army, the navy and the air force beyond soldiers dying in distant wars and a tingle when the band marches by? Is the tingle worth £45bn, more than the total spent on schools? Why does Osborne "ringfence" defence when everyone knows its budget is a bankruptcy waiting to happen, when Labour ministers bought the wrong kit for wars that they insisted it fight?

Osborne cannot believe the armed forces are so vital or so efficient as to be excused the star chamber's "fundamental re-evaluation of their role". He knows their management and procurement have long been an insult to the taxpayer. The reason for his timidity must be that, like David Cameron, he is a young man scared of old generals.

I was content to be expensively defended against the threat of global communism. With the end of the cold war in the 1990s that threat vanished. In its place was a fantasy proposition, that some unspecified but potent "enemy" lurked in the seas and skies around Britain. Where is it?

Each incoming government since 1990 has held so-called defence reviews "to match capabilities to policy objectives". I helped with one in 1997, and it was rubbish from start to finish, a cosmetic attempt to justify the colossal procurements then in train, and in such a way that any cut would present Labour as "soft" on defence.

Tony Blair, Gordon Brown and George Robertson, the then defence secretary were terrified into submission. They agreed to a parody of generals fighting the last war but one. They bought new destroyers to defeat the U-boat menace. They bought new carriers to save the British empire. They bought Eurofighters to duel with Russian air aces. Trident submarines with nuclear warheads went on cruising the deep, deterring no one, just so Blair could walk tall at conferences.

Each weekend, the tranquillity of the Welsh countryside is shattered by inane jets screaming through the mountain valleys playing at Lord of the Rings. With modern bombs, no plane need fly that low, and the jets are said to burn more fuel in half an hour than a school in a year. Any other service wasting so much money would be laughed out of court. Yet the Treasury grovels before the exotic virility of it all.

Labour lacked the guts to admit that it was crazy to plan for another Falklands war. It dared not admit that the procurement executive was fit for nothing but appeasing weapons manufacturers. No armies were massing on the continent poised to attack. No navies were plotting to throttle our islands and starve us into submission. No missiles were fizzing in bunkers across Asia with Birmingham or Leeds in their sights. As for the colonies, if it costs £45bn to protect the Falklands, Gibraltar and the Caymans, it must be the most ridiculous empire in history. It would be cheaper to give each colony independence and a billion a year.

Lobbyists reply that all defence expenditure is precautionary. You cannot predict every threat and it takes time to rearm should one emerge. That argument might have held during the cold war and, strictly up to a point, today. But at the present scale it is wholly implausible.

All spending on insurance – be it on health or the police or environmental protection – requires some assessment of risk. Otherwise spending is open-ended. After the cold war there was much talk of a peace dividend and the defence industry went into intellectual overdrive. It conjured up a new "war" jargon, as in the war on drugs, on terror, on piracy, on genocide. The navy was needed to fight drug gangs in the Caribbean, pirates off Somalia and gun-runners in the Persian Gulf. In all such "wars" performance has been dire, because each threat was defined to justify service expenditure rather than the other way round.

Whenever I ask a defence pundit against whom he is defending me, the answer is a wink and a smile: "You never know." The world is a messy place. Better safe than sorry. It is like demanding crash barriers along every pavement in case cars go out of control, or examining school children for diseases every day. You never know. The truth is, we are now spending £45bn on heebie-jeebies.

For the past 20 years, Britain's armed forces have encouraged foreign policy into one war after another, none of them remotely to do with the nation's security. Asked why he was standing in an Afghan desert earlier this year, Brown had to claim absurdly that he was "making London's streets safer". Some wars, as in Iraq, have been a sickening waste of money and young lives. Others in Kosovo and Afghanistan honour a Nato commitment that had nothing to do with collective security. Like many armies in history, Nato has become an alliance in search of a purpose. Coalition ministers are citing Canada as a shining example of how to cut. Canada is wasting no more money in Afghanistan.

Despite Blair's politics of fear, Britain entered the 21st century safer than at any time since the Norman conquest. I am defended already, by the police, the security services and a myriad regulators and inspectors. Defence spending does not add to this. It is like winning the Olympics – a magnificent, extravagant national boast, so embedded in the British psyche that politicians (and newspapers) dare not question it. Yet Osborne asked that every public service should "once in a generation" go back to basics and ask what it really delivers for its money. Why not defence?

There are many evils that threaten the British people at present, but I cannot think of one that absolutely demands £45bn to deter it. Soldiers, sailors and air crews are no protection against terrorists, who anyway are not that much of a threat. No country is an aggressor against the British state. No country would attack us were the government to put its troops into reserve and mothball its ships, tanks and planes. Let us get real.

I am all for being defended, but at the present price I am entitled to ask against whom and how. Of all the public services that should justify themselves from ground zero, defence is the first.