LP5/50 now section 5.

[Powderfinger]

Many of the airguns that look like real firearms are not semi-auto's even though they mimic semi-auto's in appearance. Their mechanism is operated by a pull of the trigger akin to a double-action revolver.
Most such guns are pellet firers but some fire BBs or can fire pellets or BBs.
Some of the airguns that look like real firearms are semi-auto's in that they prepare for firing the next BB by the blowback mechanism of the slide after the first shot has been fired by double-action or the slide has been racked or the hammer has been cocked.
Along with the semi-auto pellet firers that have been used for ISSF-style events for decades, there are hundreds possibly thousands of these guns in circulation.
If semi-auto airguns really are now Section 5 then presumably there will have to be a massive round-up and prosecutions of the owners. B
ut the authorities do not seem to have advocated such a round-up.
Which makes me agree with RobinC that semi-auto airguns of less than the 12fpe/6fpe limits are not Section 5, have never been Section 5 and have not suddenly been legally declared section 5...