Ask HN: How does the London startup scene compare to NYC?

I'm British, and currently living and working for a startup in NYC. I love the city and my job is great, but I'm starting to get to the point where I want to start doing my own thing sometime soon. I've got ideas and the ability to execute on them (I'm a developer) but it's extremely difficult for me to set up a company and work for it- and as far as I know it's impossible for me to do it on the side of my existing job.

So, I'm starting to wonder if I should move back to the UK. Is there anyone out there that's spent a decent amount of time in both, and could give an account of how they compare?

It feels like NYC has a hackathon event every weekend and an active social scene to back up the industry- not to mention a ton of investors on hand to pitch to. Can the same be said about London?