The possibility that Scotland could have voted to leave the
UK raised many difficult questions, not least of which was a
constitutional crisis in the UK. But the ripple effects of a
split would have spread throughout the EU.
This is because Scotland voting to leave the UK would have
made it much more likely that the rest of the UK would vote to
leave the EU. Part of the reason for this is that Scotland is a
more pro-European country than England. But it's also a result