If you can get the inner door panels off not to difficult at all by the way. Remove the plastic sleeve from lock and remove actuator with a size 8 spanner bit fiddly not bad though. Then look to the door side of the lock and you will see a small gap in the body of the lock below a small brass coloured lever with a squareish hole in it. Jimmy a small screwdriver into this gap and the lock should release. You can then remove old lock and replace with either a new or second hand one. I got two from a scappy for £20.00. Takes about 25-30 mins to do the whole thing.
Hope this helps anyone who has this same problem.