Well, the title says it all, really. I just don't know what credibility ICM think their published voting intention figures can have when they ask for people's country of birth, and then fail to weight by that measure when it turns out that their sample is completely skewed. Just 73.6% of their weighted sample was born in Scotland, whereas according to the census results the figure should be roughly 81.5%. English-born people account for 16.6% of the sample, whereas it should be 9.6%. You'd be forgiven for thinking that ICM believe this is a trivial matter, but in fact country of birth is still one of the strongest predictors of referendum vote - in this poll Yes lead by 52.2% to 47.8% among Scottish-born people, while No lead by 75.6% to 24.4% among English-born people.
My rough calculation suggests that if country of birth weighting had been applied, the No lead among the whole sample would have been just 51% to 49% - that's before the turnout weighting (which helps Yes slightly) kicks in, and that in turn would have been likely to take us to roughly Yes 50%, No 50%.
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YouGov have published a poll for Sky News asking about issues like the currency and more devolved powers. I'm guessing these may well have been bolt-on questions from the voting intention poll which will be published tonight, in which case it's clear from the cross-breaks that No are likely to have some kind of lead in the headline figures (but probably not a huge one).
UPDATE : It seems from what I've seen on Twitter that YouGov are still polling, so perhaps the 2000+ respondents from the Sky News poll will only make up about two-thirds of the 3000 sample that is apparently expected. In that case obviously the calculation is thrown up into the air again - it could be better or worse.