I think it depends mostly on how much you value faster access rather than whether the NHS is sufficient for basic healthcare. NHS access can cover your normal GP and hospital needs, but private insurance can be useful for specialist consultations, diagnostics and planned treatment when waiting times become an issue. I came across this UK-specific ExpatInsure guide international health insurance in United Kingdom while looking into the same question, and it explains how international cover can work alongside the NHS rather than replacing it. If you also expect to travel back to the US regularly, I’d pay attention to the geographic coverage too, because that’s where international insurance can offer something a UK-only policy doesn’t.