Hi Gazandlucy.
This is going to be a cat/pigeons moment for the regular contributors here, but putting the cooker control switch inside a cupboard will not break the law or contravene any regulation.
However, installing the switch yourself without firstly jumping through a few council hoops and paying the fees will break the law, beware!!
Might i guide you toward searching through a few of the many topics about LABC notification and suggest that it will be easier for you get a self-certifying sparky in to quote for the work.
You might get a shock (no pun intended

) when you find out how much the fees are for your local council to check/approve DIY work in the kitchen.
Maybe a few of the faster typists/copypasters here will provide further info on this.
IMO it removes a big unsightly switch from the wall and gives you less stuff to clean around when you get the inevitable cooking residue on your splashback.
Again IMO, you should have a switch conviently located for the purposes of maintenance ( e.g. removing all power to hob when cleaning around the controls/switches) and ideally my preference is to install these within 2 metres of the device. However, there is nothing to say you cannot put it inside a cupboard.
As a matter of convienience, i would locate the switch in the adjacent cupboard, near the top and near the front. This means even when the cupboard is loaded up, the switch can still be operated without being hidden behind pots/pans/Jif/mr.muscle etc and is unlikely to be accidentally operated, allowing you to switch it off once every ** for cleaning.
** insert appropriate frequency, depending on how mingy you are
