Investment in Blood, written by Frank Ledwidge, a civilian adviser to the Government on Afghanistan, claims the war, which has lasted more than a decade, has cost Britain at least £37 billion.
And the outpouring of cash is not over yet. By 2020, Ledwidge estimates Britain will have spent at least £40 billion on the Afghan campaign.
That's much higher than the current MoD estimate of £25 billion and way above the official figure given for the cost of the Iraq war - £8.3 billion.
According to the Daily Telegraph, it is also equivalent to the cost of hiring 5,000 new police officers or nurses and paying for their entire careers.
Investment in Blood, which will be published next week by Yale University Press, is the first attempt at a full audit of the Afghanistan campaign.
According to Ledwidge, who has also been a civilian adviser to the British government in Iraq and Libya, Britain's military presence in Afghanistan's Helmand province has proved particularly costly.
It also claims that, based on UN and NGO reports and "collateral damage" from air strikes and gun battles, British troops in the province have likely killed at least 500 non-combatants, with roughly half of these officially admitted.
Ledwidge told the Guardian: "There are no new lessons here, only one rather important old precept: before you engage in a war, understand the environment you are going into, precisely and realistically what it is you are trying to achieve and will it be worth the cost? In other words have a strategy."