Polo 1.4 TDI X Reg Central locking

My Polo's central locking is activated by turning the key. Recently it broke and I wondered if anybody can diagnose the problem.

When locking the car you have to lock both the doors independently. when unlocking the car you can only unlock it via the passenger door.

It seems as though something has broken inside the Drivers door but I cant even see how to get the door cover of and I am worried about damaging it. Can anyone offer any advice as towards the possible problem and how difficult it is to get the door skin panels off?.

Am I wasting my time?. Should I just take it to a VW dealer.

Cheers

Ned