Although you can get 20 amp switches the cooker normally is more than 20 amp so unlikely you can have cooker with rest although there may be a make which goes over 20A.
The grid system allows switches and fuse holders all in the same back box, but likely needs a deep back box and all very good when doing a re-wire but to move could be more trouble that it's worth.
As to what an electrician is prepared to do, that's up to him, there is some lee way as to how regulations are interpreted. But in real terms you don't need any switches, you could switch off using the MCB/RBCO in the consumer unit, only rotating equipment with a motor over a fixed size needs an isolator within sight of the machine, however common sense tells one a switch to defrost a freezer without needing to empty the fridge part to pull the unit out makes sense.
If you have an earth leakage fault having to drag out washer, etc to unplug it to test what has gone wrong is not really what you want, in the kitchen here where the consumer unit is in the kitchen by the door with fire or any other emergency simple enough to remove power, but rest of house the consumer unit is under the stairs, not a good place to isolate in an emergency, so you need to do a risk assessment for your house, the electrician who wired the kitchen in this house clearly did not think about what he was doing, the hob isolator is directly behind the hob, so a chip pan fire one would not reach isolator but as said CU is easy to reach.
Be it weight loose on washing machine, or tumble drier on fire, you want the option to turn off at some remote point but not too remote, but not covered by regulations often a gas cooker has no isolator even when it has a higher fire risk. It is up to you to work out what you want and compare the cost so decide what your going to have.
