Adding a one way switch to existing cable to light

Hi - I'm hoping this is fairly simple but I have cable in the garage which comes out of the rose in the picture and runs along out of the door to a PIR light. I would like to add a switch though.

Am I right in thinking I need the cable to go into the switch and wire the live into a terminal. And then have another cable with the live into the other terminal and splice the neutrals together.

a) is this OK?
b) what should I do about earth? The switch and back box is plastic but the light is metal
c) for my new cable to run from the switch to the light - what should I use?

Any advice would be great.

a. Yes
b. Join them together in a block at the switch.
c. 1.0mm twin and earth cable.

Add another cable to the junction box and run that to the switch.

It will require some alteration to the wiring in the box.

My X-ray specs need new batteries. Take a pic of the wiring inside the JB.

Thanks Winston1.

EFLImpudence, I was going to use the existing cable which runs from the junction box to the light. Ie Wire it into the switch and then run a cable out of the switch to the light. I didn't fancy fiddling around with the junction box.