It's a kind of circular argument where both sides are partly right. One set of laws says we can only have 22LR semi auto, but that would have been written when semi auto sub 12 fpe airguns weren't envisaged. Because of that, and the statement that Lassmann issued, it follows that no prosecutions will be forthcoming. In that respect, it may be unlawful to possess a semi auto, but the law is not going to pursue you over it.
Many laws are out of date and don't get changed. We've had this situation for 15 years or more, and the "earliest opportunity" hasn't arisen yet. If there was a public vote to win by seeking a change in the law, one party or another would have been telling us all about that for the last three months during the election campaign. So there is no detectable desire to change the legislation.
We still have a law that requires every London cab driver to have a bale of hay on board in case the horse gets hungry. I haven't seen a prosecution lately.
We also have two rifles widely held that would be section 5 if they went over 12fpe. The TX 200HC and the early model BSA Ultra, both with barrels under 12 inches long. Why are AMTA and GTA not demanding that AA cease production and BSA recall all the 10 inch Ultras? Because the illegality would be a technicality; they are airguns, end of. Why cannot some folk accept that semi auto under 12 fpe is also a technicality?