There was a very awkward little moment in the Commons just now, as the terrier-like Labour backbencher Tom Watson asked the Treasury team about the role of Andy Coulson, the former News of the World editor who is now a media adviser to the Prime Minister, David Cameron (there was a distant "hook" about "consultants").

After a slight hesitation, it fell to Danny Alexander, the Lib Dem who is the Chief Secretary to the Treasury, who looked only a little uncomfortable when he merely said that Coulson "works in No 10" and that Alexander would get back to Watson further if required.

The moment passed with a few laughs. But it is indicative of the kind of trouble that may lie ahead of this unlikely alliance.