I lived in the UK for a few years. Luckily the UK tax system is super easy, all PAYE (Pay As You Earn), so if you only have a job and no major investments, you don't have to file taxes at all. They've already been collected in the proper amounts throughout the year from your paycheck.
The US taxes all worldwide income, so you'll always have to file a US tax return. However, the US has agreements with many countries (UK included) that exempt you from being "double-taxed" if you are under a certain amount.
The limits for individuals is $91,500 and for married couples $183,000. This amount includes deductions that you can make for housing, utilities and relocation costs. For London, the maximum housing deduction is over $80,000.
You automatically get a 2 month extension to file and pay your taxes if you are living abroad.
You should also go back through all of 2010 and determine when you were in the US and when you were in other countries. You'll need to document your travel in order to meet the physical presence and bonafide resident tests.
Check out Publication 54 from the IRS - http://www.irs.gov/publications/p54/index.html
Also this site has a pretty good breakdown of how it all works - http://www.taxmeless.com/IRS593Publication.htm
You'll also need to file TD F 90-22.1 if you have any foreign accounts worth over $10,000 at any point in 2010.