Running a spur off a cooker circuit?

[bongos]

Have a look here. This work would be notifiable due to its location.

The socket is already in place, therefore it is not a new install. I'm just providing the supply from another source, also in place as part of original house build.

If you are supplying this socket from a different circuit you must make sure that the two circuits are do not end up connected anywhere. In practice it would probably be safer to install a new socket outlet from the CCU (as you suggest) and just leave the existing one as it is. Otherwise you may have problems terminating the cables from the existing s/o at the same location.

OOI, when you say you can't terminate the cable for the existing s/o used for the dishwasher - is it possible with a deeper back box that you could?

This might be the best option of all. then you can just leave everything as it is....