Yeah I know but its allot higher than I feel comfortable with. On a hard run, i.e shopping and a car full of people she likes to sit between the M and the R, so half the 3/4 on the scale. The M is the highest I want it to go and with the thermostat opening at that its just not cricket in my books

Put it into diagnostic mode and check what the actual temp is. As tooly said M is in the middle of normal.

Have you checked to see that the AC core is not blocked with s**t and the air can't flow through.

Are you sure the Radiator core isn't blocked, with you record of Mechanics I wouldn't take his word on it, ie you specialist with the head, etc.

If you are still worried put a lower opening thermostat in it and be done with it.