Thought I'd do a little update in case anyone's interested.
I finally got under to have a look. The wires are sleeved and not accessible. The sensor is the only thing I could touch. So I might try the fuses. I might have a go at the pump myself. I don't mind paying the labour but imagine the garage would want an OEM part. They are about £180 . The cars got a dodgy flywheel, overdue timing belt, a few other problems and been around the block more times than an Essex girl. Not sure if you can get one from the breakers though.
Also the glow plug circuit has thrown up a fault code again. Doubt it's connected to this secondary coolant pump though. Cheers.