I think the main reason why British voters flocked to the Conservatives was because of well-founded fears that any Labour govt would be extremely dependent upon the SNP for support, which would have allowed SNP to drive the govt from the back seat in pursuit of its separatist agenda.
Meanwhile, the left-leaning Scottish National Party cleaned up in Scotland, winning 56 out of 59 seats. This leaves Britain's parliament sharply divided along ethnic lines, with the SNP in power in Scotland, and Conservatives in power everywhere else. It also raises the possibility of pressure for another referendum on Scottish independence.
Cameron, meanwhile wants a referendum of his own - on pulling the UK out of the EU. If he succeeds in doing this, then EU will have received a mortal blow that would jeopardize its survival, so that any independent Scotland would not even be able to join EU's embrace.