Doniwales, here's my tip: READ. Go to
www.dfes.gov.uk and have a look at the free publications. Request copes of any and everything that sounds relevant to you. Study them. Read the DFES site and visit the links to Key Stage 3 Strategy and National Curriculum Information. Read about teachers unions. Go to
www.amazon.co.uk and order Sue Cowley's 'Guerilla Guide to Teaching'...it will tell you the basics of working in the UK schools.
I advise you not to seek a teaching job through an agency. Good schools turn to agencies as a last resort. It will be better for you to use The Times Educational Supplement to look for work, and make cold calls to the good schools in your area. Apply directly.
Get in touch with NARIC and have your qualifications verified as UK equivalent (that would be your high schol diploma and university degrees). Your US teaching license does not count here, so do research about the Graduate Training Programme's employment-based scheme for Overseas Trained Teachers (OTTs). When you interview, express your desire to fast track that programme and gain QTS (Qualified Teacher Status) as soon as possible. For interviews, you must be able to use UK teaching jargon comfortably, so you are going to have to study, but your studies will show you that things are pretty much the same here, just the jargon is different. It will come down to the fact that you know you can do the job but they might not be sure than you can, and your saying, well, I'm not from here but I know I can teach is not going to be good enough. So do study! Know more about your situation and what will be required to get you up to the same level as any other UK teacher than they do. Be confident and knowledgeable.
I got a job here on my own and earned QTS, so this is all from experience. PM me with anymore questions you may have.
Good luck!