Why it matters:
1) You only get taxed on income earned in the UK. If you had workdays outside the UK, AND did not deposit your paycheck in the UK, that income will be exempt.
2) The cost of your housing may be exempt under "detached duty releif".
3) Given the above, it may pay to see a UK tax accountant to help you determine the amount of rebate you may be entitled to.
In addition to the above, your income earned outside the UK (US bank accounts, US securities accounts, rent on your US house, etc) is tax exempt unless you bring it into the UK. This is also true if you are ordinarily resident, so it's not one of the differences.