Just to give my 5ct. being not in the UK, OIII 2014, 1.6TDI
I had my 5 speed 0A4 gearbox repaired under warrantee at 75k km because of the noise, especially in the cold morning, clearly heard first 200metters drive.
at first visit to the garage they add 100ml oil and said in most boxes is was the reason. However, not in mine. then they replaced four bearings inside... but never less, it appears that the same gearbox is not very new, and on the latest models has been tilted by 12deg causing bearings not to be covered by oil level enough good, hence similar noise is coming.
Same noise came back to me after another 40k km, then simply add 100mL 75W grade oil and noise gone, however it was what I experienced in my case.
Not to claim 100% proper information: I have read that the recommendation was to fill 2.3l oil instead 1.9l originally and found another VW recommendation (true old, but seems very relevant to) to use oil with spec G 055 726 A2 for 0A4 gearbox.
Recently, I changed the gearbox oil with Castrol V one, 2.3l added after full drain (taking out the fork pin), so far so good, almost no recognizable difference when change gears