Hi Bexs

To answer your question

Light Circuits – 1.5 mm2 – 2 core + Earth

Switch Wire – 1 mm2 – 2 core

Power Circuits- 2.5 mm2 – 2 core + Earth

I recently done a job for 2 clients who wanted to save on labour charges and ran the cabling themselves under my instruction. But this was agreed to prior them doing it as if they had come after the fact I don't think I would have got involved.

So I would recommend talking to a couple of local sparkies first and sounding them out.

Good Luck