I know I need a gas safe engineer to fit the new thermocouple, but I want to make it easier for him and therefore save me money. I can't get access to the part without dismantling the whole cooker. Any suggestions?
I'd advise you not to dismantle the appliance, because I guarantee it wont cost you a penny less.
It's better the engineer takes it apart so he knows how to put it back together, because it needs to be put back together by the engineer so that he can leave the appliance in a safe condition. He wont want an easy thermocouple change, followed by a puzzle with half the screw missing.