I just reset all the counters within the trip computer. I'm not sure if there was a service function in there, but I reset the lot. There wasn't a spanner icon, but there was a symbol with a car going past a racing post type thing. Various versions of that including one with an M, one with a G, etc, some of which were not even in the car's handbook, were all reset to zero.
The SERV light is now off! I even drove around for a few minutes, parked up, switched off, then on and drove around again and parked up again.
This seems to have done the trick. However I'll monitor it in the next week, hopefully it stays off.
(now for the next things on the list, tailgate button popped out, broken wing mirror, water in the overhead switch console, failed bulbs behind clock display