Update, in a nut shell - Warning has gone at no cost.
Fortunately I know a garage who are Audi/BMW specialists, I popped it round and he cleared the warning on the dash. Restarted the car, warning came back. He rescanned it but couldn't find any warnings or issues despite the dashboard still showing the alert. He fiddled about rescanning and restarting the car. Then gave the ad-blue tank a couple of knocks with a mallet (technical fix) and he heard the pump kicking in!
Couple of more scans and restarts of the engine, the fault was still there on the dashboard.
He suggested it may need a software update and maybe a new ad-blue tank, but suggested I give it a good run first. Went on the motorway and after 7.8 miles exactly, the alert on the dash disappeared!
Pulled over at a services and stopped the engine, locked the car up and waited a minute or two, started the car, no fault! Went to the supermarket and did the same, came back to the car, no fault! Went home and left it for a few hours, popped to top up with fuel, still no error, amazing!
Just got back from giving it a good run into North Yorkshire and back again for the weekend, still no reoccurrence of the fault.
I'm driving an Audi A6 2014 S-line, Ultra Black edition with 71k on the clock. I did refill the ad-blue a week or two ago (which I've noticed quite a few people reporting this problem have also done before getting this).
My recommendation is not to run to Audi straight away, but take it to an independent for a once over. My experience with Audi is that they tend to shotgun and problem by just replacing the part immediately.
For example my washer liquid was leaking and they quoted me £600 to fix, but I knew it just needed a new jubilee clip to hold the pipe together.... I fix that myself for £1.37 and I am by any means a mechanic. Audi didn't even look and were going to charge £60 for a troubleshooting fee.
