Roofing Regulations for Large Roof Using Marley Flat Tiles

[phil28]

Hi a little professional advice would be great.
when fitting a new roof of large Marley flat tiles, on a semi abutting rosemary tiles, the tiles on the hidden gutter I believe require 2 mechanical fixings either by the 2 screw holes or by another type of clip or wire device, question is this a legal requirement no quibble, or is it a guide line?
next when you have a hip end the tiles under the hip tiles, do they too legally require 2 mechanical fixings, finally the tiles below the ridge tiles , are they too screwed?
and lastly when adding tile and a halves to the rosemary side to create the hidden gutter as they are not part of the new roof but a small modification to an existing roof, are they screwed of just hooked on.

thanks for any answers, would appreciate no guess's