Extending a lighting cable ?

[Spinny]

Looks like the sparky has left us with a lighting cable for a locally switched wall light which is too short for where we want to site it.

How can the cable be extended these days ? Is it acceptable to use some form of in-line connector buried in the wall ?

(in the safe zone of course)

[ProDave]

Crimp or solder and then heat shrink insulation.