Well of course the current lovely weather starting to expose some flaws in the cooling system.
Recently fitted new thermostat to deal with engine running hot (95C - 100C). Fresh coolant mix, all hoses checked and where necessary, replaced.
Since then temp. has sat nicely in the middle with a 1C to 2C variation either way depending on situation. Great, I thought - sorted!
However out comes the sun, on goes the air-con and engine temp starts rising to 100C+. Switch off the air-con (completely, not ECO) and temps go back to normal.
So a pretty conclusive connection between air-con and engine temp.
AC does pump out cool air, no funny smells or noises. At times I have noticed a change in tone from the compressor upon starting especially when the engine is hot but that's the only thing I've noticed.
Any hints much appreciated, MOT next month and I'm having a major service beforehand so this may discover the problem. But just in case its something obvious and known I'd thought I'd give a shout.