One of my teammates was registered with the PA as number 1104.
As the first 200 numbers were reserved for Refs that means he is the 903rd player to register with them, that was yesterday afternoon so pretty up to date figures. Although PA registration is not (yet) necesary to play in leagues other than the MPANL it is free and many non MPANL player and teams are registering.
This is something that should increase, as player registration is passed from the UKPSF to the PA. Also, with many of the UK leagues starting to follow the PA rules this season, it may be that player registration becomes encouraged by these leagues if not required.
If this is the case the number of PA Registered players will become closer to the total number in the UK.
Individual UKPSF membership is usually in the low hundreds so that would not be so usful a statistic.
But i reckon the 1500 to 2000 estimate is about right. Of course it depends on what criteria you use to define a tourney player. Is someone between teams that hasn't player yet this season, how about someone does regular sup'air walk ons but never full blown tourneys? What about someone who trains regularly but is having a break from playing?