Well, Artic, unfortunately not that housing.
It turns out it's the thermostat housing on the new water pump that I had fitted not more than 500 miles ago. There was a problem at the time as the thermostat housing that was supplied had different stud / bolt holes to the pump. It was returned and the one on now looks new. There was talk of not being able to get the right part but Rimmers,
https://rimmerbros.com/Item--i-GRID001740 , seem to have it .
Garage taking it back in on Monday and I trust them but it could start to be awkward if I'm expected to pay for something that they did / couldn't fix properly at the time.
It looks like tricky to get to.
Wife's going to kill me.
JohnnyBG