Hello everyone. The issue has finally been sorted!
The new tank arrived along with pump/sensor/heater unit. The garage I had arranged it with let me down at the 11th hour. Reluctant to wait any longer I pulled out the tools and went at it myself. The hardest part was probably getting the hoses off. That and a 10 minute wait for the AdBlue to drain
.
The pump seems to have a newer part number than the one I had in my car. Once secured, the rest was done via . It seems like the issue didn't go away until I drove the car for about half a mile.
I do still need to completely top up the tank as I only had a 10 Litre/2.2 Gallon one at home. I'm happy that the issue has been solved though.
@DrPeter
As you suggested, I also replaced the injector to the latest variant.
All in all it was a pain while it was present but with help from you guys, it's been sorted. So thanks very much for the help. I guess the only thing that needs doing now is an software upgrade.