The number is about 25 according to Steve Houghton. This comprises 12-13 by Bedfordshire police, at least 2 by Durham/Northumbria Constabulary, and at least 2 by Hampshire Police. Hampshire Police also released a single shot target rifle in a wooden stock which I have seen, but I don’t think that counts.
There are also a few later PM rifles, which I’m not sure of the origin. I imagine it was a lesser known batch of ex-police PM rifles. There are also some, much fewer, PM rifles of other origin, but not ex-police. I can only recall 4 or so genuine L96s legally making it out into the wild. Two are re-captured rifles.