A friend has his electric hob connected to his cooker switch and the
electric oven running off of a 13amp plug.
He wants to get rid of the electric oven and get a new one that
specifies that it must have a fixed power supply (presumably a cooker
switch).
If the cooker switch has the spare capacity, can we just use a heavy
duty junction box to run both appliances from the same cooker
switch?
Also, this being a kitchen, does the work have to be done by a
certified electician?

Thanks for any advice.

Brendan.