It's safe BUT:
be careful to install a switch (pull cord if it's in the ceiling and you won't pull wires around, or run wire to your current wall switch and place one there)
If your devices are wired directly protect the system with a fuse (FF2A is more than adequate to protect both), or just use standard UK plugs that are already fused.
Also remember to check if you have both phase and neutral at ceiling box (old code: phase is red and neutral is black new code: phase is brown and neutral is blue).
Check also not to take power from the switched circuit (otherweise you'll be able to use your stereo only if lights are on).
Pleas post a photo of your box so we can try to help identifying the wires.