Welcome to the forum Wayne, you'll find the members on here are a friendly and helpful bunch :)
Id say the fault is linked with the drivers door barrel. On some Audi's the locking system is controlled by the drivers door locking mechanism and if this fails it can cause the central locking to not work properly.
I had a similar issue on my a6 where ,the drivers door locking mechanism started to fail and the car wouldn't unlock properly. I had to have an auto electrician replace the drivers door locking mechanism which cost me around £120.
Hope I've helped :)
Cheers
Steve