Wiring Up New Single Point Spot Lights on Conservatory Wall

[maxcars1]

Now that the conservatory is built I need to sort the lighting. Originally I had a PIR light 300w on the outside running of a wall light within my dining room - this was the way it was wired since a new build in 2003. Anyways the light switch has 2 cables running into the back box: 3 reds running to the switch, earths going the the back box and nuetrals running to a choc block. The circuit running to the PIR is now redundant as I'll be mounting the Air Con evaporator on the wall where the PIR was. My question is can i run 1.5mm lighting circuit from the back of the switch out through my cavity into the conservatory cavity to run my 3 single spots and disconnect the redundant PIR circuit?

Other ideas was to spur off ring in conservatory with 3 amp fuze and then put a new switch on the wall, but I'm looking for the easiest option here. Clearly not a sparky but aircraft engineer, so any advice would be appreciated.

 

[hairyben]

Sounds fine to me except for running it through the cavities- frowned upon. Obviously total load must be considered when adding lights but if you've removed the 300w I can't see that being an issue.

Or, you could spur it off the landing light.

I'll get my coat.

 

[maxcars1]

So can anyone advise how I wire these 3 spots up to the original switch if this is plausable? Oh and how do I know which is the lead in the sitch that was connected to the PIR which I have choc blocked to make safe outside on the wall.