I suspect there may be a problem with the engine coolant temp sensor or associated wiring/connections.Ok to drive ,but just check coolant level with engine cold.hth

Here's a bit of an update, it's a bit strange. The coolant level is a little below MIN so I'll be topping it up - have some Halfords Advanced coolant/antifreeze.

I went out in it this morning and it started OK but the temp gauge didn't move. However, when I turned off the engine the gauge needle moved to the middle (which is where it usally is after a few minutes) and went to the cold position after completely turning off the ignition. The fan was operating for most of the drive (but not straight away).

When I came back to car after half an hour it started but the revs dropped and it nearly stalled. It seems a bit odd to say the least.

All this started after filling up with petrol but this is probably a coincidence?

It's been mended by the Ford garage! The wiring to the ECTT sensor had rotted and needed repairing. Thanks for your advice everyone!