Mains voltage downlights (UK)?

Question:I'm installing mains voltage downlights, what type of wire do I use? 2 or 3 core?

Any tips would be appreciated as I'm going to have a bash at it but haven't done it before

Thanks in advance!!

Answers:
well in the us we don't call it core we call it gage

on down lights or can lights you can have a max of 15 can lights 100 watts each most of the time down lights or can lights are ran with a # 14 romax (its a white cable)

# 14 size wire 15 amp max load
# 12 size wire 20 amp max load
# 10 size wire 30 amp max load
# 8 size wire 40 amp max load