Hi! I'm so sorry. I don't think I ever got notified of your reply! We had a great time. He didn't drive my car but when he moves here, presumably he'll have to take his UK test?.... 
Glad you had a good time
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When he moves to the UK, he will be legally allowed to drive on his US licence for up to 12 months from the date he takes up residence. If he wishes to drive after those 12 months, he will need to have passed all the UK driving tests and have received a full UK licence.
If he hasn't got his UK licence by the time the 12 months are up, he will be treated as a learner driver and will only be able to drive with a provisional licence, L plates on the car, no motorway driving, and he must be accompanied at all times by someone over 21 who has held a UK licence for at least 3 years.
So, it's a good idea for him to get started on the UK licence, driving lessons and doing the tests as soon as he can after moving to the UK, so he has enough time to get the UK licence within the first 12 months
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