That’ll teach me to not proof what I write in my lunch break 
yes, I was talking amps!
As I said, I was talking about the lighting in my house which is a standard two up two down, and only 4 gu10s on the circuit in question, and I did consult an electrician.
As always, if in doubt, get someone qualified in!
Absolutely on board with overspeccing where possible 
In my case however I was doing in situ cable pulls without replastering, and an extra 2mm of cable (plus sheathing) would have made at least two of the runs pretty much impossible! I don’t know what the original builders were thinking, but they definitely didn’t leave much room for future changes.