How many more times do we have to state on this forum ...the fuse within plug tops is for the protection of the supplied flexible cable, ...NOT the appliance!!! And NO the warranty of the appliance would not be void if a fault within the appliance goes bang!! These manufacturers supply the exact same appliances all over the world, and most such countries do NOT have fuses within the plug tops!! There is absolutely nothing stopping the OP from using a double connection plate fed from the cooker control unit to supply both cooking appliances.
All this crap about cutting a moulded plug of a cable voids the warranty is total bull, it is just a ploy by some of the so called warranty providers, to illegally fail to perform their duties under the manufacturers warranty terms. Any appliance connection to the utility supply conforming to BS7671 by a competent person/electrician cannot be deemed as misuse or alteration to void a warranty, ...End Of!!!