Katpaint,
I started living in England legally in March 2003, and got my full driving license July 2005. I was over 7 months pregnant at the time!
As far as I know, there is no entity that goes around and checks immigrants to make sure they're driving on a full British license after a year. The only problem you may have is filing a claim with your insurance company, if need be.
Go to WH Smith, buy a DVD to assist you with the theory test and book your theory test. After passing the theory test, you have a year or more to take your driving test.
You will feel so much better after you get this out of the way. After I passed my driving test and came home, I popped open a beer and phoned my Mom at 3 a.m. her time to tell her the good news!