In the UK, one of the most common tax efficient savings tools is an Individual Savings Account (ISA for short). However, if you are planning on staying in the US permanently, ISAs are not recognized by the IRS so neither capital gains or income from ISAs, are tax free.
This UK ISA E-book covers all you need to know in terms of holding an ISA whilst living in the US and why you should consider repurposing your investments towards compliant, and potentially more tax friendly solutions.