Basically I know you'll probably all say 'head gasket ' but could it really be anything else?

The stage one fan doesn't come on (Bitron unit or knackered thermostat? Both?), but the stage two does but by then it's like blowing against a hurricane and the temp keeps climbing. A run at decent speeds does bring the temp down again but when it's climbing into the red the air coming through the blowers seems to get cooler making it next to impossible to bring the temp down.

Could it just be the lack of phase one fan and an airlock somewhere? Can I bleed the system myself? if so, how?

It's going into the mechanic for further investigation on Wednesday. I'm dreading it TBH.

i had the same problem and it was a sensor in my rad, changed it and problem solved