My house was built in 1971 my mother's in 1972 both have 1.0 lighting circuits. I have worked on multiple houses some are 1.0 some 1.5 none of this means too much.I moved into a new developer house in 2001 - I am not there now. All houses were wired in 1.5mm lighting. Until LEDs became the norm, I have never come across any new build or rewire using 1.00mm lighting cable. Not one. I am not making this up. Your experience is 100% the opposite of mine.