As you say, this appears to be a common fault with JLR diesel engines, with many possible causes that are bringing up the fault message. Unfortunately some many dealers over-rely on diagnostic tools without sourcing the cause of the problem.

If you want to try and tackle the problem yourself, you may find it worthwhile to invest in an OBD tool so you can read and reset fault codes yourself. Possible causes for the fault may be an overfilled AdBlue tank, degraded AdBlue fluid, a blocked AdBlue injector nozzle, EGR valve or NOx sensors, all of which are potentially fixable but it will still require some time and investment.

Alternatively we would recommend finding an independent JLR specialist, who at the very least will offer a cheaper diagnostic service and will have likely encountered and solved this problem on numerous vehicles before.