Stay in London, and study in the evenings if you want. Benjamin Franklin said "three removes is as bad as a fire", meaning there's a high cost to rebuilding your social network. I'd guess it would take you about 18 months to fully build new friendships. I moved to a non-ideal city for work (twice!) and it set my career back by a couple of years. The cost of living in Glasgow is lower because people are happier living in London.

If you want to fully maximize utility, you're making a false choice by just looking at the two jobs. Get back in grad school and work as hard as possible until you're in the top half of the class at a top school (or otherwise meet the "great hacker" criteria that Paul Graham describes on his website). Then, start a fast-growing startup with one or two other outstanding hackers. When it stops growing after two to ten years, sell out. Then, you should be in a really high-utility space where you can do massive good and/or enjoy novel luxuries.