"Scots supporting British teams"
I'd say the vast majority of Scots support any English competitor in sport against a foreign opponent and likewise with club football teams when they are playing foreign opposition. The exceptions being the English national football and rugby teams. I have an English wife and it of course irritates her somewhat that I don't actively support England when they are playing but the reason for that is the local derby thing involved and the fact that in both rugby and football they are the oldest rivalries in the world and one of the most intense. Admittedly in modern times the English may have lost that intensity in regard to the football rivalry as the likes of Germany and Argentina became bigger fish to fry, but it still exists in Scotland. Asking a Scot to support England is akin to asking a Rangers fan to support Celtic or vice-versa. Most probably won't do it. I've seen people say to their English friends "oh yes I hope they win" in order not to offend them but then sit down with big cheesy smiles when the other team scores. So basically when you see these polls saying lots of Scots would support England I'd take them with a pinch of salt. What people say they would do and what they actively do can be different things.
Of course in regard to this thread Sootland and England are completely seperate concepts in the football world. Scots tend to naturally enjoy Scottish victories and vice-versa for the English.