It is time that we copied the French and built a truly independent British nuclear bomb. It might cost a bit more – or we might decide to go for something cheaper and more compact. But what’s the point of a hugely expensive nuclear strike force, if we don’t truly have the last word on whether to use it? Because we don’t really own our own nuclear deterrent.

Here’s why. I won’t lightly forget the day Margaret Thatcher exploded in a 150-megaton mushroom cloud – because somebody had told journalists the terrible truth about Britain’s supposedly independent nuclear deterrent. The Trident missiles at the heart of it aren’t really ours. It happened in late October 1987 and for weeks afterwards it was said in the corridors of the Ministry of Defence that the Iron Lady ‘wanted blood’. Like all the best and truest stories, it was immediately officially denied.

There was even a clash in Parliament about the leak – during which it was rather desperately claimed that the missiles were like Calor Gas cylinders, which are swapped over when empty. This homely comparison did not alter the facts. To save money – about £700million in those long-ago days – we were sacrificing a key part of our nuclear deterrent’s independence. We were also risking British Trident missiles being caught up in some future disarmament deal between the US and Russia, concluded over our heads. For Moscow might sneer that ‘our’ missiles weren’t even ours, just part of Washington’s arsenal.

The truth was revealed by a senior civil servant. The new Trident missiles we were preparing to acquire would not actually be owned by Britain. They would merely be rented from the US. Most people know very well the difference between being a freeholder and a tenant. This was a major step down from the 1960s deal made with the US, for Polaris rockets, which we owned and maintained ourselves. That’s why this information had never been supposed to come out.

The official revealed the facts to defence correspondents at the Coulport weapons depot, an ultra-secret part of the Faslane nuclear submarine base. He said: ‘The missiles are American… we’re not having to buy the missiles from the Americans. We’re sharing them.’ He added: ‘With Polaris we own the missiles and process them in the UK. We’re renting the Trident missiles. We’re paying for them but we’re renting them, not buying them.’

Even more unfortunately, he compared the arrangement to leasing a car. The truth was – and remains – that British nuclear submarines must queue up at Kings Bay in Georgia to hand over Trident missiles for maintenance. Then they must be given fresh ones by the US. This is not really independent. For what if an American president became so cold and hostile towards us that he blocked the arrangement, leaving our Trident submarines empty and defanged? In 1987, few could conceive of such a president. It is not so difficult now.

What if an American president became so hostile towards us that he blocked our arrangement, leaving our Trident submarines defanged? In 1987, few could conceive of such a president…

A 1987 scandal revealed our new Trident missiles would not be owned by Britain, but merely be rented from the US. (Pictured: A Trident missile is test-launched from a US Navy submarine)

Remember, Britain’s nuclear arsenal was originally built to tell the US where to get off. In 1946 our tough Foreign Secretary, Ernest Bevin, came back from America furious at the way he had been bullied by his opposite number, James Byrnes.

He growled, during a key Cabinet committee: ‘We’ve got to have this… I don’t mind for myself, but I don’t want any other Foreign Secretary of this country to be talked to or at by a Secretary of State in the United States as I have just had in my discussions with Mr Byrnes. We’ve got to have this thing over here whatever it costs… We’ve got to have the bloody Union Jack on top of it.’ He won the debate. The Bomb was built.

Since then, thanks to technological failures, American changes of mind and economic crises, that Union Jack has got a bit faded and tattered. Rather than reassert our sovereignty, British politicians have preferred to conceal our lack of it.

The 1987 row, which for many reasons is seared on my memory, is largely forgotten now because soon afterwards the Soviet Union collapsed, and the fear of a Third World War receded. And after that, a Labour Party that had once been crammed with nuclear disarmers suddenly became the fervent supporter of a British bomb. I have always thought that they only ever objected to our nuclear weapons because they were aimed at Communist Moscow. As soon as Moscow was no longer Communist, they couldn’t care less.

But now the issue is much wider. Britain has spent a tremendous fortune on making its own Bomb, and keeping alive the capacity to do so. It has spent a second fortune on building and running the submarines that carry that bomb – and a third fortune on first buying Polaris and then leasing Trident, the missiles to deliver that bomb. In a world that is more nervous and dangerous every day, it would be crazy to throw away what we have. But it might make sense to ensure that, from now on, our deterrent is all ours.

Our columnist envies ‘the gigantic silent black bulk of the French ballistic missile submarine Le Temeraire’, pictured here at Ile Longue base in Brittany

The Liberal Democrat leader Ed Davey made this point at the weekend and he deserves credit for it. The two main parties have long ago stopped thinking about the issue, and new thought is badly needed.

I felt rather jealous a few days ago when film emerged of France’s President Macron standing in a vast hangar at Ile Longue in Britanny, with the gigantic silent black bulk of the French ballistic missile submarine Le Temeraire below and behind him. Before singing La Marseillaise a cappella with hundreds of men and women from the French military, he proclaimed simply: ‘To be free, we must be feared. And to be feared, we must be strong’, which is the basis of good defence in any language.

By contrast to our American-equipped nuclear missile submarines, with their rented rockets, Le Temeraire and the rest of her Triomphant class carry 16 M51 missiles that are entirely designed, tested and built in France. The same goes for their warheads, whereas Britain’s nuclear warheads are, let us say politely, very closely based on US designs. The French submarines are backed up by a squadron of Rafale fighter-bombers which can deliver nuclear bombs, a capacity Britain gave up in 1998. They now also carry air-launched nuclear-tipped cruise missiles. France’s nuclear ‘Force de Dissuasion’ is not subject to any command outside France, not even Nato. The French President alone decides when and where to use it.

Yes, the French force is significantly more costly than ours. But as a result it is surely a much more persuasive deterrent. And the giant price of retaining and renewing Trident, said by some to be as much as £205billion, is a lot to pay for a system whose on-switch is effectively property of the Pentagon.

In any case, there is surely an argument for Britain to retain a smaller, more compact and less ambitious nuclear force than Trident – which is really a scaled down superpower cold war system. Israel, which anyone must agree faces more pressing dangers than Britain does, runs a much more modest nuclear arsenal. The danger of leaving things as they are is that we may simply not be able to keep up the payments on a weapon that is not, ultimately, ours.