No, you don't turn it in here. keep it updated for when you are back living in the US again. Most states let you renew it online nowadays,, I would definately not let it expire.
One thing,, the standard UK driver test is for a standard shift car. If you are driving an automatic, and are not staying longer than two years,, I would just arrange to take the test in automatic, altho, then you legally can only drive automatic over here if you are alone in the car. It wouldn't hurt to take a few lessons with an instructor, to help you get ready for the test.