I say don't do it. When you live abroad you can miss certain things about england, but in your post you realise all the shit things about London - they are still there but now you dont have your relaxed foreign lifestyle. It could also be that people have moved on - maybe your crazy sense of hunmour is less fun for your pals who have to travel 1.5 h home on the tube.

Re programming: its not that easy to just to walk into a job. Yes the salaries are high, but they don't just take folk off the street. They will test you. Can you write an Olog(N) complexity sorting algo in 30 mins based on a problem you have never seen before?

I would suggest staying abroad and finding expats to get a taste of home. All the things you hate about london might be be here but worse.

I would do a bootcamp somewhere cheap like BCN or berlin or even eastern europe. Then you can get a low paying job in a cheap place to live. Once you have one or two real jobs under your belt then maybe come back to london and get high paying one which will be a million times easier.