More British soldiers die in Afghanistan. How long will voters tolerate this?

Is one life worth more than another? Does the death of any individual human being count as more significant, more tragic than any other? Of course not. But some deaths attract more attention than others. Sometimes it's the manner of that death: murders draw the vicarious eye more than a peaceful end at home among family. Sometimes it's the nature of the deceased: need I say more than the words "Princess Diana"? And sometimes it's the context of a death.

The Ministry of Defence has just announced the deaths of two British soldiers, men of 1st Battalion The Duke of Lancaster’s Regiment, in Afghanistan. Their passing takes to 297 the number of British service personnel to die in Afghanistan since 2001.

Within days, that number will rise again, and due course it will reach 300. Logically, that number should be no more significant than any other. The suffering of the family of the 300th fatality will be no more or less dreadful than that of the first or the 117th or any other. Each loss is uniquely awful, and yet of precisely equal weight.

Drop a dozen (or 300) lead-crystal wine glasses onto stone and each will splinter and shatter in a different way. But each each diminishes us all by exactly the same measure. Yet the human imagination is drawn to round numbers, in defiance of logic or even good taste. Numbers are how we understand the world, how we quantify and contain a universe that would otherwise be frightening in its scale. Numbers make infinity a little easier to bear.

So when the 300th death is announced, it will catch the imagination more than the two fatalities today. It will lead television news bulletins and newspaper front pages. It will feature in conversations at dinner-tables, in offices and pubs in a way that many others have not.

Soldiers, who live with the idea of death, can find the media focus on numbers and "milestones" puzzling or even offensive. Yet these are the facts of human nature and modern culture. You make not like those facts. I may not like those facts. But facts they remain. And anyone who is serious about politics must deal in facts.

Certainly, ministers and officials are aware that reaching 300 dead will present a new challenge for the Coalition over Afghanistan. David Cameron made a nod to this in the Commons yesterday when he warned: "We must be ready for further casualties over the summer months."

Public support for Britain's continued military presence in Afghanistan is already weak: a ComRes poll in April said 77 per cent back in immediate withdrawal. What will similar polls say after the next "milestone" moment? Public opinion (usually) drives political opinion. Some Liberal Democrats already take the view the the UK mission must end sooner rather than later. Better to leave the fighting (and the dying) to the Americans, some say, noting that President Barack Obama is in any case talking about reducing US troop numbers next summer.

In the Labour Party, criticism of the Afghan war is now commonplace. No one will be surprised if one — or more — of the candidates for the party leadership comes out in clear opposition to another of "Blair's Wars." More surprising, and potentially more significant, is the number of Conservatives with grave doubts about the Afghan war. The sober analysis of men like Tobias Ellwood and Rory Stewart is proving persausive on the Tory backbenches.

Ministers are acutely aware of all this, and plan to step up the Government's communications work, trying all the harder to promote the successes and benefits of the continued deployment. Louder than ever, they will proclaim that our servicemen do not die in vain.

Yet underlying these preparations is a clear sense among senior people in the Coalition that Afghanistan is something to be managed and brought to an end as quickly as possible. There will be no unseemly rush to the exit: any withdrawal must be presented as victory with honour, not a scrambled retreat. The way in which Britain left Basra looms large in many memories, both civilian and military.

Earlier this week, one person who has discussed Afghanistan with Mr Cameron recently told me the PM sees the conflict as "Blair-Bush legacy stuff", a problem he inherited and wants to outlast. That attitude has persauded some of our senior military people that "we're out in a year," or at least that the British mission in late 2011 will look almost nothing like the one that exists today: UK forces will indeed leave the combat ops to the Americans, and switch almost entirely to training and mentoring Afghans.

"We are six months into an 18-month military surge," Mr Cameron told MPs this week, tacitly appealing for another year's forebearance and sacrifice. But will British voters, who pay the Afghan bill in blood and taxes, stay that course? Sadly, the Coalition will soon face its first real test over Afghanistan.

(PS. I am aware some people might find my analysis here callous or tasteless. Indeed, speculating about the deaths of our fellow citizens isn't pleasant. For any offence, I apologise utterly. But I have friends who serve and have served in Afghanistan, and friends who wait at home for word of loved ones in theatre. I am fully aware of the committment and sacrifice of service personnel and their families.

In my experience, they are among the most hard-headed assessors of situations like this. We fail them if we let sentiment cloud our judgement or limit our political debate about a mission that arguably matters more to them than anyone.)