The wording of the 17th edition does not outlaw the practice but it would still be hard to comply. It does not give examples and is worded in very general terms. An example is:- [quote]314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device. [/quote] This may be deemed as saying you should not do it but it does not make it that clear and if you want to argue with some one over the way that it's wired it may be hard to quote a regulation saying so.
Clearly it should not be wired that way but it's not easy to prove since one is allowed to leave wiring as it was when the regulations are upgraded.
Years ago it would have been illegal in the days when different charges were made for electric for lighting and electric for power as lighting was charged at a lower rate but this stopped well before I was born some time between the two world wars I think.
It was common when I was a lad to see women plugging their iron into the lights clearly dangerous as there was no earth.
So although clearly it should not be done. To find the regulation stopping it would take some finding.