Is Muammar al-Gaddafi a "legitimate target" for the coalition? Liam Fox was swiftly rebuked by the US when he suggested  as much on Sunday. "We are not going after Gaddafi," the US navy vice-admiral Bill Gortney told a press conference at the Pentagon.
But in an interview  on the Today programme this morning, William Hague refused to rule out targeting the Libyan leader. He said:
It all depends on how people behave. The targeting that we do on these kinds of strikes will always be in accordance with the UN resolution and that of course emphasises the protection of the civilian population.
In other words, the removal of Gaddafi could be justified as a by-product of the coalition's mandate to protect civilians. But such loose talk has already upset the generals. The chief of the defence staff, General Sir David Richards, has robustly declared that Gaddafi is "absolutely not" a target. "It is not allowed under the UN resolution and it is not something I want to discuss any further," he said.
So, on only the third day of military action, we already have a major split between the armed forces and the government. It's a sign that the tension between the formal aim of civilian protection and the coalition's underlying desire for regime change (Cameron's repeated declaration that Gaddafi "needs to go") is growing.
The need for clarity on this point is urgent – Cameron must provide it in this afternoon's Commons debate.