That would actually be allowed AFAIK - it's the bath/shower that makes it a bathroom (both in British English usage and electrical regs!) and banishes the white goods. But WCs tend to be v. small (as if given a little extra space architects say What shall we do, Fred, cupboard or loo?) so can't house them either.

Usually (flats/small houses aside) they'll be in the scullery (adjoining the kitchen) though, not actually in the 'cooking area'.