kateg60

How is this managed, buy a one way flight to the UK even if you know you may return to the US the same year for a holiday? Which passport to use leaving US and entering UK? Does anything have to be done when leaving the US? Overwhelmed and nervous....

Pulaski

The only "passport check" leaving the US is by the airline who want proof that you will be allowed into the UK when the airline takes you there. So if you have a one way ticket (note, a return ticket may be cheaper) show them your British passport, as that is the one that allows you to stay indefinitely (a US passport holder without a visa, needs a return, or onward ticket in order to be allowed into the UK). Given the law regarding US citizens (always using their US passport to enter and leave the US), you can show both UK and US passports if you want to.

On arrival in the UK, show your UK passport at the immigration kiosk, so you're not admitted as a visitor.

On traveling to the US later in the year, as a US citizen you cannot get an ESTA, and so will need to show your US passport at the airline desk when you check in, and then enter the US, as legally required, using your US passport. On the return leg to the UK, show/use your UK passport as described previously.

And just to be clear, nobody tracks or cares that you arrive and depart using different passports, not in the US and not in the UK.

excpomea

'note, a return ticket may be cheaper' Without a doubt.
We purchase returns when cruising across the Atlantic.

was about 50% of a single flight.