I've got the pressure switch coming any day now so will let you know if this solves it for me. If not gona buy the solenoid.
Did this solve your issue?
Hi, very sorry I never updated . Turned out in my case I was lucky as when I got under the car to fit an ac solenoid valve (pressure sensor didn't solve it and is fitted from above but reading on you'll see why it didnt solve it) I noticed the sensor for the solenoid had been left unplugged by the mechanic who fitted the thermostat a few weeks earlier! So this was why my ac wasn't working all along!
I have got a pressure sensor, the crows foot spanner needed to fit it and an ac solenoid valve you could have for a reasonable price though now if you're interested.
Edit: just noticed you had your thermostat changed too, get under and have a look. Mine was very obvious as the sensor was just hanging there disconnected.