Back home from holiday so first day since the MOT I have had a chance to check her out. The pleasure of getting through the MOT was tempered a bit by the fact she overheated again on the way back home. So first thing to do was check that.
Soon found out why she overheated, she took 4 ltrs of water/antifreeze to fill up :-) My overflow bottle was also full of water. So I emptied that back into the expansion bottle and then took her on a 20 mile run out to see what happened. She behaved herself but the temperature profile didn't seem to be 100% right. Back home I checked and the overflow bottle had some water in again. Now she shouldn't be overflowing at those temperatures so the first suspect has to be the pressure cap on the expansion bottle. So compliments of Amazon overnight, got a new cap this morning and fitted it. Now need to see how she goes on the next trip.