If all of your income has been from the US the way you avoid double taxation by the UK is often by "resourcing" the income as foreign on Forms 1116 and 8833 ane electing to claim credit for the UK tax paid.
US designed software may not be designed with UK pension plans, UK tax years, child benefit, FBARs, child trust funds, PAYE etc in mind. They may still be great, but remember that the interaction with UK tax rules can still be confusing!