It is the design or adaptation that is the issue, not the fact that it happens to expand, or the marketing style. If this were not the case then every plain lead bullet would be S.5, which would somewhat bugger up all the lever action gallery rifle lads. When I owned a 45/70 it used nothing but ordinary lead bullets. There is no doubt that they would expand greatly if they hit the right parts. but they were not S.5. Likewise at the other end of the scale, the ordinary .22 rimfire round made of soft lead and will certainly expand if it hits the right part. But neither is designed to expand. Like A-Max, they will expand and are regularly used, and advertised for the purpose in the USA I believe, for hunting live quarry.
Of course, I don't doubt that some police officers, and some Firearms Licensing Officers too, somewhere would be daft enough to give it a run in the OP bullet, but then I am aware of at least one FLO who thinks that shooting solid ball from a S.2 muzzle loader is illegal
. But, I am confident enough that it is not S.5 that I would happily show it to any police officer who was polite enough to gain entry into Chez Shootist and point out that I had no authority to possess S.5 in that calibre. It could be quite fun.
I discovered the bullet in the OP when I was sold a box for light .308 loads (15 grains of Unique) by one of the most anally retentive firearms dealers I have ever met. There is simply no way this dealer, who has more than 20 years in the business, would have ever sold these bullets to me if they were S.5. This, of course, proves nothing, but he remarked himself on the issue, and so had clearly studied the matter.
So, can you use the OP round (assuming it's not S.5) or A-Max to shoot deer in England and Wales, if all other conditions are met? (I'm not asking about whether they are the most suitable round, just whether it's legal.)
If you don't have to give up your car because other people commit crimes in their cars, why should I have to give up my firearms because other people commit crimes with their firearms?