Forget scottish independence...
London is in more need of independence...or we are in more need of independence from it...
So why not make London (well, everything inside the M25) into a city state, leave it to raise it's own taxes, build it's own airport in the estuary etc. - you could even extended it to the South East if that made sense.
Then you move all of the UK institutions out of London, revitalising other UK cities - this includes UK government, which could go to Birmingham/Manchester (or even a virtual parliament shared with Edinburgh/Cardiff).
Job done.