Ok, so an update....
I called the local Audi dealer and checked if they had the part in stock and they had 1 left (part number ending in B) which I reserved.
It cost me £84.42.
I got there and spoke to the parts guy and asked if they had many people come in for this part and he said yes and one person came in yesterday with a similar problem.
To told him it's naughty from Audi as they/car dashboard are giving misleading information and he agreed.
Anyway I got home and replaced the part - it's so easy that nobody should ever need to pay anyone else to change it. It took me 2 minutes (if that)! Shame on any garage charging more than 5min labour!
Anyway, I started the car and so far I haven't had the warning light come on, but then again I only reversed a few meters back and forward in my drive. I will have to take it for a longer drive later when the roads are clearer to confirm that it's sorted!
Looking back, the fact that the start/stop function was intermittent for a while maybe was a sign that there was a fault/sensor was failing, before the actual dashboard gave a warning!
I would highly recommend getting a obd scanner too (which I recently purchased a couple of months ago) and it really helps to narrow down the issue and search on the net for advice - that's how I found this forum!
Many thanks to all those who have contributed to this and the other main thread!