Woo.. more Bristolians - where are you?
The bit about the memory sounds very, very unlikely. There is no diagnostics on the windows, and certainly nothing to stop them working completely. It's going to be a bit of your own diagnostics afraid. When it's not working, check for voltage at the switch, and check the switch is switching ok (I think it simply goes from no resistance to infinite resistance). Then you may be on to checking the voltage at the motor, taking the door apart etc.