Well, after initially accepting the job (because I didn't have much time to consider, so it would have gone otherwise), I had a think, and it would be best to stay where I am right now-- considering the job market, it would be a little bit daft to give up what I have now. That, and my contact on this flat is for another 5 months, and not 3 as I originally thought!
My main priority is to try and find a decent place to live, and to try and improve the social side of things. I think that the door isn't completely closed at the place that offered me the job, so perhaps in the future something else will come up. I'm sure that either this year or next year I shall be back in London, but it would probably be best not to rush things and do it on a whim!
Thanks for all your words of wisdom, it's good to hear what other people think :)
(job was at the BBC, by the way)