Libya: Is cost of military mission sustainable?
As Britain flexes its military muscle at Col Muammar Gaddafi alongside international partners, it's the human not economic cost that is foremost in people's minds.
But with the government intent on saving billions of pounds and with no clear exit strategy in Libya, just how financially sustainable is the mission?
Prof Malcolm Charmers, from defence think-tank the Royal United Services Institute, says the cost will fluctuate dramatically depending on which direction the mission takes.
"If the war goes on for a relatively limited time - weeks rather than months - then we're talking about relatively small sums - at least compared to Afghanistan, which costs £4bn a year," he said.
"If this goes on for less than a month and is primarily air-powered, then hundreds of millions at most. The cost could start rising sharply if you had significant ground operations."
He said the war could be lengthened if there was a stalemate on the ground between the rebels and Libyan government which the coalition could only break with ground action.
Prof Charmers pointed out that in the 1999 air war against Serbia in Kosovo, Nato became frustrated with its ineffective military strikes and increasingly began to target infrastructure.
That meant the number of sorties, and therefore the cost, remained high - a scenario he doubted for Libya but could not rule out.
Over the past few days, Britain's military firepower towards Libya - and inevitably its costs - have been growing.
A Royal Navy Trafalgar class submarine has been firing Tomahawk cruise missiles from the Mediterranean, and Tornados have launched long sorties from RAF Marham in Norfolk.
Typhoon jets are on standby in Italy, Hercules planes have been mobilised and two Royal Navy ships have begun a naval blockade.
Air-to-air tankers are needed to refuel the Tornados, then there are surveillance aircraft, Airborne Warning and Control Systems (Awacs), service costs, and the possible deployment of special forces.
Prof Charmers says the cost of a single cruise missile is about £500,000, while a single Tornado sortie is about £30,000 - in fuel alone.
If a Tornado was downed, and had to be replaced, it would cost the Treasury upwards of £50m, he warned.
The US and UK have already fired more than 110 cruise missiles, but it is not clear how many were launched by Britain.
Drawing comparisons with Afghanistan and Iraq, the professor said any ground operation in Libya would probably be shorter and easier to get through.
"The big cost in Afghanistan and Iraq was not the fighting at the beginning but the occupation that followed," he said.
"If there was quick military action [in Libya] to help rebels or protect the civilian population, the cost would not be enormous providing it was short lived."
He said the current costs were "sustainable" and "containable" as long as the conflict had sustained public backing.
"Cost is not the central issue, the central issue is whether we are seen to be carrying out what we set out to do.
"It's whether people agree with the mission and whether we are achieving that," he said.
The action in Libya follows the government's strategic defence review last October, which outlined cuts of £4.7bn over four years, with defence spending falling by 8% in that period.
When questioned on Monday whether the military action in Libya would be funded from the Ministry of Defence (MoD), a spokesman said: "It's too early to say how much it [the conflict] will cost, and therefore where the money will come from."
And a Treasury spokesman said on Monday: "Further work is being carried out in relation to the potential costs surrounding this operation.
"Depending on the size, scale and associated costs of the operation, the MoD has the ability to seek additional funding from the HM Treasury Reserve for the net additional costs to Defence."
But on Tuesday, Chancellor George Osborne confirmed to MPs that the cost would be fully met by the Treasury's reserve.
He said the MoD estimated the operation would cost tens rather than hundreds of millions.