My field is English literature <snip> I'm wondering what the job market is like for English PhDs there, after a post-doc. I'm aware that it's more competitive than the US, but is there at least a decent number of lectureships that open up?
To answer the first part of the OP's question: English lit is a very, very difficult field to get a lectureship in at the moment. It is better in language/linguistics, and better still in film & media studies, but if you are a straight-down-the-line lit person then, in my humble opinion, you will have a much better chance of finding a permanent post in the US. Yes, of course it's a highly competitive field in the US as well, but as the US is so much bigger than the UK there are more jobs out there, and therefore more that will fit your qualifications and research areas. There have been very, very few posts coming up at entry-level lecturer grade for English at all in the past few years. This is probably an RAE-related malaise but, to tell the truth, I can't see it changing until at least a few years after the RAE (as depts will have used their new-hire budgets up on higher-level hires so as to scoop senior scholars with high quality publication lists).
Sorry if this is depressing news, but if you have the right passport to live and work in the US, for heavens sake take advantage of the larger number of jobs being advertised in English! Many of us in the UK can only dream about being able to work there.