I am assuming a 32A radial circuit.
Unless the Manufacturer's Instructions state otherwise-
4mm²
(2.5mm² would suffice, but omitting overload protection for this fixed load)
As echoes has pointed out, if the appliance is new it should come with manufactures instructions. These instruction will give you the information that is needed regarding device rating and cable/flex size. They normally recommended a heat resistant flex between Cooker isolator and appliance.
Something like H05RN-F, H05RR-F 3181TQ or 3183TRS. Looking at the output you have given, I would expect a 2.5mm2 flex to be specified.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local