Libya protests: No-fly zone - bluff or reality?
In the corridors of Britain's Ministry of Defence a planning taskforce is busy working up contingency plans for a possible no-fly zone over Libya.
It is part of the gathering international momentum towards isolating Libya's Col Gaddafi amid fears he may once again use his air force against his own people.
But is it practical? Is it desirable? Or, as some cynics suspect, is this just playing for time in the hopes that Col Gaddafi soon yields to pressure and steps down before a single Western warplane is sent anywhere near Libyan airspace?
How would it work?
If a no-fly zone were to be established then the core countries would probably need to be the UK and US, just as they were in Operation Southern Watch in Iraq throughout the 1990s, where US and RAF jets flew daily sorties to deter Saddam Hussein from attacking the Shia in the south.
But signals coming out of Washington show that the Pentagon is not keen.
The US Navy currently has two aircraft carrier groups in the Mediterranean region - vast, floating air bases that can project enormous firepower right along Libya's coast.
The UK has an air base at Akrotiri in Cyprus, where a squadron of Typhoons could theoretically be stationed. But that would be more than 1,000 miles (1,600km) away and there are far closer runways in Malta, Sicily and mainland Italy.
One possibility is that the RAF's role would be confined to support - such as mid-air refuelling.
What are the obstacles?
They are numerous. What would be the legal basis of such an operation? Its backers would ideally like to get a UN Security Council resolution behind it but would Russia, France and China agree?
The UK Foreign Secretary, William Hague, has indicated that a no-fly zone could be imposed without such a UNSC resolution, but this could split the international coalition now ranged against Col Gaddafi.
The logistics and costs of running such an operation would be huge. Where would it be based, who would pay for it, who would provide the aerial "overwatch", the airborne command-and-control needed to police the airspace?
Then there are the rules of engagement. In what circumstances would a coalition warplane shoot down a Libyan one?
Would the ban apply to all aircraft or just military, fixed-wing or helicopters? What about civilian airliners suspected of bringing in mercenaries from Libya's African neighbours?
What are the risks?
Enforcing another Western-backed no-fly zone over a sovereign Arab and Muslim country is controversial.
Many of Col Gaddafi's opponents, including defecting air force officers, say they want it without delay. Others have specifically called for the West to keep well away.
There is a banner doing the rounds in Libya that reads: "No foreign intervention. Libyan people can manage alone". Undoubtedly Col Gaddafi would make maximum capital out of this "imperialist intervention", portraying it to his population as all part of a "US-Zionist plot" to subjugate his country.
After the debacle in Iraq, this is not a place the UK necessarily wants to be.
Then what about Libya's air defences? Would they have to be destroyed first? Probably yes, in which case Libyans would almost certainly die from Western military action. Again, this is a rocky road that governments in Washington and Whitehall will have to think very carefully about before embarking on.
So are they serious?
On Tuesday night, Mr Hague was asked this question on the BBC News Channel.
His answer was that the UK had to plan for a major military escalation by Col Gaddafi against his own people.
Of course, he said, we hope that Col Gaddafi bows to pressure and steps down, but in the meantime we have to work up plans so we can act if we need to.
My interpretation? There isn't really a lot of appetite for this no-fly zone but the possible alternative - sitting on our hands while Col Gaddafi sends MiGs and helicopter gunships to kill his own people - would be worse.
Hence the plan being readied to be put into the prime minister's drawer in case it is needed, even if they hope it doesn't come to that.