Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
First question; where do you actually reside?
well HMRC will not be terribly happy! If you live in the UK for more than 183 days in any one tax year you are liable for UK taxation on your world wide income. Any US taxes will, under the Double Taxation Treaty between the UK and the US, be allowed as a tax credit against the UK liability on the same income stream.
What you must now do is to get in touch with your local HMRC office, you can find that in the Phone Book or on line, and arrange for the relevant forms to be issued to you. On completion and return that Department will tell you how much tax and National Insurance is owing and how and when to pay.
I do hope that you have found my reply of assistance.