Has my roofer put my tiles on properly?

[saveasteading]

This is within that useful document::

 

Mortar bedding should never be laid directly onto the lead, as the expansion and contraction of the lead with temperature will quickly crack the mortar. Instead, the mortar should be laid onto an undercloak of slate, tile or fibre-cement board to allow movement between the lead and the undercloak.

 

Presumably there is a formal version of this somewhere. either from the tile manufacturers or a BRE doc or similar.

 

Seems pretty fundamental. Do not lay mortar on lead.