But don't run 2.5mm before a 13A fuse - otherwise it is not correctly
protected.

Hmm. It's rated at 24 amps. You could use 1mm TW&E if protected by a 13
amp fuse.

Ok, I get your point... but I meant don't connect 2.5mm twin & earth to
a 32A rated circuit without a fuse. In this case he is planning to add
a fuse for the oven and I suggested 13A as this gives more options. In
this case it should be =4mm until the fuse (I'd prefer 6mm as this is
what the rest of the circuit uses) then 2.5mm after. Theoretically you
could use 2.5mm for the hob, but 2.5mm is what the manual says, so
best to stick to that.