Its all quite specific in JAR 1.335 (available on-line) that a pre-requisite is :
(b) met the knowledge requirements for a CPL(A) as set out in AMC FCL 1.470(b);
They accept the old UK CPL or BCPL exam passes if non-expired, which didn't require you to have approved training, though these exams are no longer available.
I found 3 months of spare time reading to be sufficient to pass the exams.