In commissioning the YouGov poll they have published today, the Devo Plus group were hoping to demonstrate that the unionist parties need to come up with clear proposals for more powers for Holyrood this side of referendum polling day in order to ensure that the future of the Union is secure. Alas for them, the findings looks less helpful to their cause than they might have hoped.

The poll shows the largest poll lead for the No side recorded by any poll yet. As many as 59% say they would vote No and only 29% Yes, a 30 point No lead. The previous largest No lead was 28 points in an Ipsos MORI poll at the beginning of May. Meanwhile, the last time YouGov themselves polled on the subject (under the guise of Lord Ashcroft, and also at the beginning of May), the tally was 30% Yes and 56% No, a No lead of 26 points.

True, at this point we should enter a couple of caveats. The difference between this poll and that of other previous polls is too small for us to be sure there has actually been a swing to No. The three point increase in No support since the last YouGov poll may simply be a product of the ‘sampling error’ to which all polls are subject, rather than a reflection of a real movement. Moreover, if we look across all the referendum vote intention polls conducted by the two organisations since January last year, on average YouGov have painted a slightly less optimistic picture for the Yes side than Ipsos MORI. Until now YouGov’s average figures have been 30% Yes, 56%, No compared with Ipsos MORI’s 34% Yes and 55% No.

But even if we regard this as no more than yet another poll that indicates the Yes side are failing to make any progress, the suggestion that the No side might win by as much as a two to one margin is hardly likely to make the Better Together chief, Alistair Darling, feel that he needs to pressurise his allies into coming up with a clear roadmap towards more devolution.

He will, of course, note that 56% of all voters, including around a half of all unionist party supporters, feel that those parties should set out their stalls for more devolution before polling day. He will note too that as many as 16% of those who are not currently inclined to say No say they would be more likely to give the Better Together campaign their support if they thought it would pave the way to more devolution (while just 3% say they would be less likely to do so). But at the same time if his lead is anything like as large as YouGov says it is, Mr Darling will also wonder whether he really does need to make much effort to reach out for those potential extra votes.

What perhaps might have been more effective at persuading him to do so was evidence that large number of No supporters might switch to Yes if they were to come to the conclusion that the unionist parties would fail to satisfy their aspirations for more devolution, thereby taking a large chunk out of the No lead. Alas for them, this seems to have been the vital question that Devo Plus forgot to ask.