I see no problems clearly the junction will be insulated, but that is a valid method.
There are two basic ways to wire a lamp, one use the ceiling rose as a junction box, this means permanent line at the lamp good for ceiling fans and emergency lamps. second is use the switch back box as a junction box, good for using PIR's and dimmers where the items need both line and neutral. Both have pros and cons and both can be used.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!