Alanabasset.
The two standard methods of wiring lights have the 'busy' end either in the ceiling rose or in the light switch. Often an electrician will decide which methods based on the toplogy of the building - his aim to reduce cable runs and avoid junction boxes. These two methods of wiring lights are being superseded, mainly due to the changing use of lights, such as previous posts for downlighters, or the increasing provision of a neutral in the switch for future PIR switching or the like.
For ages now the light switch had no neutral as it's not needed for simple switching of tungsten lights. More techy methods such as replacing the light switch with a PIR or some form of electronic device work better with a neutral, rather than drawing their own supply via the 'load'. If the 'load' ie the light is now low energy then the current drawn is often too low to power an electronic switch device - hence the neutral.
In your example I agree with all the posts to date. Sounds like the wiring methods doesn't conform to 'ceiling rose' or 'switch loop in loop out'. One cable into the switch comes from the consumer unit, the neutral in is carried out on the 'exit' cable along with the switched live - this cable now going direct to a ceiling rose(s) (with likely no other cables in the ceiling rose)