Solved

Just a quick update on this problem.

Disconnected the positive battery lead this morning and left off for a couple of hours whilst I did some other stuff. Put the lead back on and now the engine management light has disappeared and the fan is operating as normal. The system must have needed to reset itself I guess.

Only small issue now of getting the circlip back into place to hold the replacement temperature sensor firmly. It's a bit of a squeeze in there - seems to be a job for small fingers (or a micro surgeon).

Nevertheless, I'm very happy. First time I've ever done a water pump - job completed for less than £50