This is very annoying, bad practice and there is no excuse why a professional electrical installer shouldn't use a different pair of colours in the cable that runs from the ceiling rose to the light switch. A different cable with yellow down to the switch and a brown up to the lamp would avoid any problem. But this cannot be a problem, only with the UK system. It will happen anywhere where they are too stingy to use a different cable colours for light switch cirtcuits.Further there is a definite danger in the british system of unwittingly grabbing the wrong wire.
This is because the wiring colour for neutral is also used for line voltage in certain circumstances (light switches).
So a wire carrying the neutral colour will be either at line voltage or disconnected if part of the light switch circuit.
The only time I have ever come across anything other than brown and blue (or red and black, in the past) has been on three core cable, used for 'hall / landing' switching which uses more than just one light switch.