Why are the English so desperate to keep hold of Scotland? It's the oil, stupid. An estimated 90% of the UK's share of North Sea oil lies in Scottish waters, and would transfer to Scotland on independence (assuming maritime boundaries were assigned according to the normal rules). As a result, an independent Scotland would be rich - and the rump UK a lot poorer (in fact, this would be the case even under "devolution max", in which Scotland would set its own taxes and be independent in everything but foreign policy).
Which is why the English are trying to scare the oil industry into opposing independence, talking up "uncertainty" if the Scots get to run their own country. Its pure colonial rhetoric, used to oppose self-determination everywhere the English Empire stamped its boot. Fortunately, in this case, it doesn't seem to be working - yet.