As the oven is supplied with a 13A plug (not uncommon) you could
either:

a) Run 6mm from the cooker switch to a 13A socket behind the oven and
plug it in, or

b) Run 6mm to a switched spur with 13A fuse (above work surface) then
2.5mm down to either a socket or an outlet plate

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