This is covered in Part G of the BR, which are to do with hygiene. The reference to them is here, but they are not recommended reading unless you are having trouble sleeping at night.
http://www.planningportal.gov.uk/england/profe ssionals/en/4000000000371.html
Being an insomniac, I can tell you that the Regs were reworded in 2000 to make it clear that there didn't need to be this double door business - a single door between the room containing the WC and a food preparation area area is adequate, provided the closet has a wash-basin contained in it. See para 1.2 if you really want to check me - its early in the document.
BR are not retrospectively applied to older dwellings, as the above post suggests.