Demolition across a phased development - Public forum - Planning Advisory Service (PAS)

Hello All, We are dealing with an enquiry regarding a phased planning application and I wanted to clarify how the demolition offset  of any buildings on the site are applied the phases. Would it be apportioned across all phases/chosen to which phase it applies/ or be linked by what is physically on the ground for each phase area?

I have consulted the Regs and Christopher Cants literature but my poor maths knowledge is preventing me from being indecisive.

Many thanks in advance,

Emma