Thanks all
According to Adrian Flux it is possible to get insurance with a US licence and no UK licence it’s just expensive to do so
The reason his UK licence has expired is that he hasn’t lived in the UK for well over 10 years (although he was born here and passed his test here) and he just never got around to renewing it – you also need a UK address I think which he hasn’t had until quite recently
But they recommended getting a UK licence anyway some time during the next 12 months. I can’t find anything that says you have to re-take the driving test if you’ve held a UK licence at some point in the past?
US licences are not exchangeable with UK ones