I have just extended my lease to five years. It was a simple process involving just one fairly short phone call.
The usual requirement is that the vehicle should have less than 15,000 miles on the clock but due to the fact that I had added a couple of expensive options to an already sizeable AP to deal with my specific mobility issues the extension was granted. My vehicle is a BMW X1 Xdrive Xline 25D auto, with 26,000 miles on the clock.
The call centre advisor was very helpful and dealt with my request in a quick and competent manner.