Guido thinks that wavering Scottish voters may be more than a little sceptical about a last minute vague offer from the three establishment party leaders. Clegg’s history on signed pledges is not encouraging. Cameron gave a cast iron guarantee of an EU referendum that turned out to have small print that let him off the hook. Labour has gone back on their pledge as well. So why should anyone trust them to deliver on this pledge?

There is also the small problem of English MPs being up in arms at the prospect of their constituents paying more taxes to buy off Scottish voters. If the parties were really serious about this and have the cross party support they claim, why didn’t they actually put it to a vote last week? Because English MPs are livid…