Getting back to the original question and not for a moment inferring there is any inadequacy in the current set up of HFT ...
At some stage this sport / pastime may have to represent itself to government or the press. It could be when the anti-shooting anti-gun lobby tries to have us all shooting pink peashooters with plastic pellets on the grounds that real guns kill etc. But at that time it would be really, really useful for somebody to be able to say, with authority: "HFT as a sport has grown from [this] to [that] in the past N years. There are X adults and children shooting, who are learning safe gun use, and it is a sport popular with women and children, with family membership making up Y% of clubs."
The various shooters insurance companies, the shooting magazines, the manufacturers, the RFDs and BASC can only guess. As far as I can see, UKAHFT has the best chance of answering that question, but "dunno for sure" isn't going to be of much use.
Would it be a major problem to require all clubs affiliated to UKAHFT to make an annual return regarding numbers?
Of course the risk is that UKAHFT might indeed become an "official body" for the sport, rather than an organiser of events and arbiter of rules. And please understand I don't for a moment mean to trivialise anything that the current organisers do or have done.