OK, if you want to do PIRs not only do you need the bits of paper, but you also need experience,
this means years, not days or weeks, competence can, and will, be based upon your experience alongside your paper qualifications,
so in order to do periodics properly you will be expected [by your peers in court] to have not only the relevant C&Gs but also to have been mentored by an experienced electrician for a period of not less than 5 years IMHO
HTH