Leon,
You only get a pension at 55 if you retire at 55. If you retire (PVR) before 55 it remains an EDP until 65 - (I am in that category).
This page has a pdf download link for the AFPS05 booklet - page 27 addresses early departure and page 28 explains what happens if you rejoin:
https://www.gov.uk/government/public...dance-booklets