I'm sorry things didn't work out for you. London is very expensive and the job market is really tough right now. I would have been in the same position if my husband had been laid off - we'd either be going back to the US to live in my parent's basement in Colorado, or living in my in-law's basement in London.
I don't know what it is (I blame the recession), but the job market in the UK is dire, especially for foreigners with previous experience in higher level jobs. I remember another poster here mentioned she couldn't find a job with a great deal of experience, and I was in the exact same position. I had a great job in the US, a high level of education, and in the UK, I couldn't find anyone that would hire me, and the jobs I was looking at had very low salaries. I started out looking for jobs equivalent to what I did before, was told I didn't have any UK experience, tried graduate level jobs, was told I had too much experience, then tried retail jobs, and was told I had no retail experience.
I'm sure once you're back in the US, things will be much better for you in terms of jobs. Best of luck to you!