Starting in 2026 the UK no longer allows British Citizens to get an ETA to enter the UK on an American Passport. They must use their British Passport to enter the UK.
The problem I’m seeing that I can’t get a straight answer to is by US law any US citizen must enter and leave the US on a US Passport. So with that being the case how is a dual citizen with two passports meant to fly from the US to the UK?
But when you arrive in the UK they will ask you “why are you coming here?” and if you answer “I live here, my life is here, my job is here, my family are here” and present a US passport with no UK visa or other documents showing permission to reside in Britain they’re going to start asking a lot more questions.