there should be a cable at the back of the existing cooker which is controlled from the cooker switch you mention. This may go directly into the back of the existing cooker or it may go to a white box and then on to the cooker.
*If it goes to the white box, all you have to do is AFTER SWITCHING OFF the COOKER SWITCH AND THE CIRCUIT BREAKER or REMOVE THE FUSE at the fuseboard. Then get yourself a single socket and remove the plate and put what is likely to be 6mm2 into the appropriate connections, there should be sufficient space to slip the single socket in behind the new cooker and slide the cooker back.
If the existing cable goes directly into the present cooker then get a socket and a deep single surface pattress and go through the same stages as above.
It can be a bit of a struggle to get the 6mm2 cable into the housing but it is doable.
The reason you have to put the single socket in is so that the oven is fused down to the 13A, if it wasnt there and you connect directly to the existing cooker supply it will more than likely be at 30/32A.
I would use the brand MK as the terminals are bigger and are generally of a better quality. IMHO
* If you are competent
** I happen not to live in the England shire so have absolutely no knolwedge/understanding how the part P regs affect you, that is also assuming that you do live in England
EDIT
even after what you have said about the current one not being repaired it should be a hell of a lot easier and les cost than what you are about to do. just my opinion loikes