Its actually in AC 61-1
10.1.3 In accordance with rule 61.37, a licence holder who has not met the requirements of rule 61.39 for a period of five years or more who wishes to exercise the privileges of a lower licence under rule 61.37(i), is required to pass the PPL air law examination prior to completing a BFR or the appropriate operational competency demonstration required to exercise the higher privileges of a CPL or ATPL (as applicable).
10.1.4 Alternatively, in the case of an ATPL only, the holder may complete the appropriate operational competency checks required in Parts 121, 125 or 135 conducted by a Part 119 organisation before exercising ATPL privileges .
So 5yrs clock restarts each time you do your BFR, not 5yrs between exams.