Nick Clegg: We are spending billions on weapons we don't need

The shortage of desperately needed helicopters in Helmand province is part of a dismal pattern: we are spending billions of pounds on weapons we don't need and too little on equipment our troops can't do without.

Britain's defence expenditure is skewed to the wrong priorities. It is still based on Cold War assumptions about the threats Britain faces, yet the conflicts of the future are far more likely to be asymmetric in nature, fought against stateless groups or to establish and maintain peace in weak or failed states. Future conflicts may well be prompted by shortages of resources as a result of climate change. The state-to-state conflicts of the Cold War era will be a rarity.

So why on earth is Britain ready to spend billions on replacing Trident nuclear submarines with exactly the same system – one designed for a Cold War scenario with the ability to wipe out huge cities anywhere on the planet? Why are we investing a huge tranche of future equipment budgets in military platforms that will be of little or no use fighting terrorist groups or insurgency?

Why do we still have so many armoured vehicles and helicopters designed for a northern European climate that seize up or break down as soon as we take them to conflict regions? And why is Britain dragging its feet on European defence co-operation that would allow us to pool resources with the French and others so we can get more bang for our bucks?

Of course it takes a long time to procure big-ticket defence items and there is no crystal ball for what risks may emerge in the future. But that is no excuse for the lack of radical thinking in defence policy. Our priorities must change for a rapidly changing world, so that we invest in what's most likely to be needed: helicopters, mine-resistant armoured vehicles, unmanned aerial vehicles, intelligence gathering systems, strategic airlift, as well as the more traditional effect of manpower.

At a time of immense pressure on public spending in every area, the utility of the equipment and the structure of our armed forces must be based on the likelihood of the threat. There isn't money spare to be squandered on outdated vanity projects.

Labour and the Conservatives refuse to ask the difficult questions or rule out big-ticket items like Trident and Eurofighter. Neither is prepared to break the taboo on these enormous spending commitments. The Government has come up with the absurd idea of commissioning a Strategic Defence Review that won't be allowed to consider the future of Trident.

Both parties are also failing by refusing to overcome anti-EU dogma so that we co-operate fully with our allies in France and across Europe to reduce costs and build capabilities. Both parties are sticking their heads in the sand, and by doing so they are letting our troops down.

The former Conservative foreign secretary Malcolm Rifkind recently showed bravery for daring to promote European defence co-operation within the Tory party, but he is a lone voice. With 2 million men and women in Europe's armed forces, half a million more than in the US, there is a huge benefit to be had from co-operation. It is simple accounting: share equipment, buy together, divide up roles and the defence of Europe will be cheaper and more effective.

The Conservatives make promises to send more troops to Afghanistan, but these are promises they will not be able to deliver unless they address these issues.

The dispute about helicopters must be the start of greater courage and candour about what we can and cannot afford in the future. Britain has one of the greatest armed forces in the world, but we are failing them. We have to stop asking them to do the impossible – fighting modern wars with equipment and resources designed for the last century.

If we duck these choices yet again, it will be future generations of British servicemen and women who will pay the price for our mistakes. That would be the ultimate betrayal of their dedication and sacrifice.

The author is leader of the Liberal Democrats