Fair enough, but by the time you get to the '3-wire point' in the wiring, you won't be able to use a single fuse to protect both L and S/L (and I would be a bit unhappy with two separate fuses, even if they would fit).If you use click mini grid accessories, you can fit a three pole isolator and a BS1363 fuse holder on a normal one gang plate.
Kind Regards, John