What's wrong here?
Well whilst thinking about the ceiling & it's plasterboard I thought I get started on sorting out the cat's cradle that is the wiring in the space above the potential ceiling.
Tracing the cooker cable and decide that there must be a split some where, there is a hob and an oven not close to each other.
Take cover off the very tired looking cooker switch and find this ...
or
In at the top, out at the top to the oven & out to the hob at the bottom.
All I can say is
!
The isolator by the oven was wired OK.
So oven working with phase and neutral reversed for a very long time!
Oh the out to the hob runs diagonally down the wall and through the concrete slab to appear under the island unit - last bit OK but diagonally I ask you?
Nick