Sorry Robert but you're wrong, you can buy a BFTA compatible SP sling at virtually any good shooting supplier and online at hundreds of sites.
The problem is, and this is what we're discussing here, is that you can't use it as intended I.e. attached to the arm and only clipped to the rifle as needed, which is how 100% of other shooters use a SP sling for their sport be it small-bore or full-bore.
That is the only issue, not the design of the sling, not any scare-mongering about what will happen to you if god forbid you fancy using a sling, just that, the usage of the sling.
You know, the funny thing is that I've seen all this before; 1984 I roll up at my very first FT club with a Theoben Sirrocco in .22, four power scope and win a Club comp with a 28/30.
Immediately, I hear that the committee at the Club want to ban my gas-ram as it's 'cheating'.
"I just told them that anyone was free to buy the same rifle?' Which didn't go down too well so I just up sticks and went to a different club.
Then there was the problem with calibre. .22 was ok, but when a few people started using .177 and beating those using .22 ( Hello Dave Stevens at Iceni circa 1984) they wanted .177 banned as well as that was 'cheating' in their eyes.
Roll on about 1987? and at an Open two bods rocked up with a prototype Shamal and cleared the course, twice. So there was calls to ban them as well as they were 'cheating'
Scopes, omg now this could be a book to itself, when the first higher mag. Scopes like the 16-24mag Tasco started appearing and people realised that it was possible to accurately range a target instead of guess the yardage, lol it was like the end of the World and the finish of FT as a sport. The fact that even higher mag. Scopes then came on the scene like the Zeiler and then boosted Leups, well that just blew the brains of the law makers and they realised that they couldn't hope technology back and that they'd better join the arms race or get left behind.
Of course it never happened and here we are thirty years later with .177 calibre, PCP's, gimp coats, high mag. Scopes et al, so really the issue of SP slings is just another one of things that people want banned or severely restricted as they're looked on as 'cheating' in their eyes.
I predict a change in the weather, maybe not soon, but eventually as you can't stop progress.