Not sure what you mean by "backing on"? If you mean you enter the WC from the kitchen then...
There used to be a two door rule between WC and Kitchen (or something like that) but I think it's now one door...
See Part G Section 1.2
http://www.odpm.gov.uk/stellent/groups/odpm_buildreg/documents/divisionhomepage/..."1.2 A space containing a closet or urinal should be seperated by a door from a space used for the preperation of food (including a kitchen and any space in which washing up is done."
You must have a washbasin in with the WC as well.
You may need to argue this one vs two door issue with your Building Control officer.