No, it doesn't end your US licence if you get either the provisional or the full UK licence.
However, once you reach 12 months in the UK, you are no longer legally allowed to drive in the UK on your US licence... so while it may remain valid, if you have not passed all the UK tests and received your full UK licence, you will not have a valid licence to drive on anymore.
While you are within the first 12 months, you are fully licensed to drive unaccompanied using your US licence (even if you also have the UK provisional).
However, if you do not have your full UK licence by the end of the 12 months, you WILL be treated like a learner driver - L plates on the car, always accompanied by someone over 21 who has held a full UK licence for at least 3 years, no motorway driving.
So, the way to do things is:
- drive on your US licence for now
- apply for a provisional licence ASAP
- start taking some UK driving lessons to learn how to pass the UK tests
- take and pass the UK theory test
- take and pass the UK practical test
If you can get all that done within the 12 months, you will be able to drive as normal the whole time... on your US licence for the first 12 months, then on your UK full licence after that.
In terms of insurance, you may have trouble finding an insurance company that will take into account your US driving history, so it's probably best to shop around/use a broker to find the best deal.
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