Thank you all so much for the replies! Unsurprisingly when I wrote that post I was at a particularly low point with regards my job, but predictably it was promptly followed by a good day so I'm feeling better about things now :) One thing I'm really happy to see is that plenty of people have given up work and loved it! I really think/hope I will be one of these people.
With regards to going back to work, my main problem with that is that this job right now is pretty much perfect for me in a lot of ways - I like the people, I get to play lots of sports (football 3 times a week, badminton twice), it's super close (just 5 minutes on a bike, plus there are showers at work) and whilst the work is challenging at times my boss and team are actually all really supportive/nice... really, I don't think I'd ever want another job after this one.
One thing I like that was mentioned above is to simply carry on mostly as I am, but safe in the knowledge that I don't need this job... my boss is really nice and flexible with things so I'm not sure I'd need the 'FU money' so to speak, but it's nice to be in the position where if it all becomes too much, I have an easy way out.
Another suggestion I liked was to treat myself with the money from the job... if I want a new car, I can easily justify it, if I want a new phone, I can easily justify it... though realistically I'm more than happy with my bike right now, and tempting as the Sony Z3C is, my Galaxy S3 is still going strong! Most of my investments are in boring old index funds, and I want to focus on those, but maybe that can be where I spend my 'treat' money on - picking some stocks and hoping they come good :)