2002 1.9 Central Locking operation with key fob - VR6
Posting on behalf of a colleague. A single press of the key fob opens drivers door, subsequent presses do not open the other 3 doors as expected.

The other three doors can be opened once in the car by pressing the central locking switch in the car.

His local VW garage have quoted £70 to have a look + any cost to fix

Not sure about the MK4 Golf, but is the key behaviour programmable? And if so, can it be programmed to only open the drivers door?
2002 1.9 Central Locking operation with key fob - rtj70
I believe it does that by default - I even programmed the locking on my Mondeo to do the same. It's a while since I had a Golf and a Passat (the Passat replaced in 2003).

To open just the driver's door it is one press. To open all doors it is two presses in quick succession. I'm surprised the VW garage does not know this.
2002 1.9 Central Locking operation with key fob - Altea Ego
the timing of your "two presses" has to be spot on. - you need to practise it.