Anne,
You shouldn't have to file UK taxes, generally only higher tax rate-type folks or those self-employed or having weird tax situations need to file. Anybody can file but unless there's some notion that you must owe or you deserve a refund (which shouldn't be for your situation) then it's not necessary to do so.
In regards to US taxes, IRS says don't have to file if you haven't earned $4,850 in the year according to this IRS link:
http://www.irs.gov/faqs/faq2.htmlIf you do need to file then there are forms for the Foreign Earned Income Exclusion which allows you to exclude all of the income you've earned in the UK from your US tax return up to $80,000. As you've not starting paying off student loans and don't seem to have any other additional tax circumstances then it should be pretty straightforward beyond that. I'm not sure, but I think you can't file the 1040EZ form because of the Foreign Earned Income Exclusion but someone might be able to correct me on that.
I use Turbo Tax myself because it does everything for me, I just have to answer their questions and then they build the form. One annoying thing I found is that the US Gov't won't let you file electronically if you are filing from overseas. I hope they change that soon.
I haven't done my taxes yet, I need to get onto Turbo Tax! Good luck, if you need any help I can try to lend a hand.
Matt