In Afghanistan we have 10,000 troops fighting a nasty counter-insurgency campaign with mixed success. Our soldiers are brave but even their inadequate equipment is hugely expensive at a time when the country is rapidly running out of money. A British soldier is dying, horribly, in Afghanistan every few days. Most are blown apart by clever Taliban bombs – many more are horrifically injured. In one of the gruesome paradoxes of modern military medicine it is possible to keep a soldier alive who in a previous conflict would have died on the spot. Some escape dying horribly only to survive horribly. The stories of those who battle bravely to recover have been movingly told in the newspapers and on television. The worst casualties remain hidden away.

Our presence there is justified by the Government and our military leaders as making the streets of the UK safer. That is the Reason Why. Like an advertising slogan it is repeated over and over again. Its advocates rarely show their working. Anyone smelling a rat is labelled as disloyal to our troops. But few are convinced. In the UK jihadist terrorism is rather obviously an internal threat. It's here and it should be dealt with here. Security begins at home not thousands of miles away in a part of the world the British left 60 years ago. A general election is under way and no one is talking about Afghanistan – not even about the MoD's failure to ensure that troops there get their ballot papers in time. Why?

Part of the answer lies in the nature of our political system. The main parties set the agenda. The Iraq war was a two-party stitch-up between the Labour government and an eager Conservative opposition. This time round on Afghanistan it's a three-party stitch-up.

Last summer it looked for a moment as if Nick Clegg, the star of Thursday's debate, was going to break ranks. In an article on 8 July he clearly signalled his growing unease with the cross-party consensus. The language was tough and honest: "Our soldiers' lives are being thrown away because our politicians won't get their act together." But it came to nothing. Clegg bought into President Obama's surge and his manifesto now promises that the Lib Dems will be "critical supporters of the Afghanistan mission".

The Conservative manifesto position is as you would expect from a party dominated by stay-behind neo-cons: "We are committed to succeeding in our mission in Afghanistan and will not leave our Forces without the resources they need to fulfil this goal." It's true that Gordon Brown has failed to equip our soldiers adequately despite his blustering denial in last Thursday's debate. But the idea that more helicopters and armoured vehicles will bring success suggests the Conservatives have not done their homework. A quick email exchange with the Soviet generals who lost in Afghanistan a quarter of a century ago might give some useful background to the grandly titled Conservative "national security team".

The silence on Afghanistan is also partly to do with the nature of many modern politicians themselves. Tellingly, neither man who would be prime minister on 7 May has served his country in any way except as a party politician. Perhaps Brown had dreams of life as a Highland officer with swirling kilt and claymore that were cruelly thwarted by the loss of an eye playing Rugby – in which case I am sorry for him.

Cameron's failure to prepare himself for high office with anything other than a stint as a special adviser and a spell in television PR is odd given his education. It would have been easy for him to join the army on a short service commission as so many of his Eton contemporaries did. I suspect both Brown and Cameron feel a little guilty about this given the extent and danger of our recent and ongoing military expeditions. The same probably applies to Nick Clegg. As a result they love their photo opportunities with the troops (entirely unreciprocated) but have little idea of how to run a conflict or deal with senior officers.

The most serious effect of this inexperience obviously shows up in the governing party, Labour: the command and control arrangements agreed by ministers for Afghanistan are perverse and amateur. The Permanent Joint Headquarters that runs things has to work out the best way to deploy large numbers of poor bloody infantrymen on patrol in what are essentially low-density minefields. But the man in charge is an RAF officer, as is the Chief of the Defence Staff, Air Chief Marshal Sir Jock Stirrup – as is even our chief liaison officer to General Petraeus, who runs the American show. I doubt that Nelson would have been much good on his charger at Waterloo or the Duke of Wellington pacing his quarter deck at Trafalgar but this is how we run things in Afghanistan.

The Conservative boast that they know how to run things properly rings particularly hollow after the Dannatt affair. That a serving head of the army should become so close to the official opposition is contrary to Queen's Regulations and therefore a clear breach of military discipline. Gordon Brown was right to refuse General Dannatt a peerage.

But in the end I doubt that ignoring the financial and physical cost of Afghanistan is entirely a political stitch-up. It is partly to do with us all. As our country's status in the world continues to decline we cling on to reminders of a more vigorous and glorious past. The campaign in Afghanistan may be a mistake and poorly run but the extraordinary courage of our soldiers in a gruesome and gruelling struggle far away can still inspire and comfort those of us safe at home.

The sadness is that our troops in Afghanistan have become a suffering army rather than a winning army. Their glories and difficulties bring to mind Captain Scott more than any other figure in British history. The words of a surviving member of Scott's last expedition nearly a century ago could just as well be said of our gallant efforts in Afghanistan today: "... though we achieved a first-rate tragedy... tragedy was not our business."

Crispin Black, a former government intelligence analyst, is Independent parliamentary candidate for South West Wiltshire