It could well have been Chinese whispers, but wasn't that how they forced the manufacturers to introduce AT in the first place? - Wasn't it a suggestion that the HO guidance on the definition of capable might change if the manufacturers didn't make it more difficult for their guns to be tuned above the legal limit?
I'm not suggesting they're going to do it, and I have no idea why they'd want to, I was just pointing out that it wouldn't require an act of parliament or a change in law, merely a change in the HO guidance on the definition of "capable" in the existing law.
They already have an unpublished definition of capable, I don't see how changing that definition would require them to publish a testing procedure.
This wouldn't be the first time the interpretation of the law has been changed - they changed the interpretation of the Section 660 Tax laws a few years ago which meant that husband/wife businesses had to pay more tax. Didn't require a change in law, just a change in the way they interpreted it and applied it.