An HW80 is capable of 7ft/lbs for the German market; 11.5ft/lbs for the UK market, and 18ft/lbs for the US market.

You are an idiot if you run around knowingly with an unlicensed FAC rated air rifle. The airgun community don't want such idiots, no one does.

To get prosecuted takes quite a lot to stick, but if it does stick its pretty serious. The Police and their Test centres are not allowed to force a gun to fail the tests. Always best to have a qualified gun related solicitor/barrister for your defence as the Law isn't quite so shut and stuck as some here suggest. It will cost a bomb too, with no guarantee of the result. Basically, don't go there.

For all this "threat" of prosecution it shouldn't be anything to worry about for few people are ever going to find themselves in such a difficult situation. The Police are not hiding behind every bush.
I find these conversations a put off to those thinking of taking up the hobby. Thousands upon thousands enjoy the airgun sports and never have any such problems, as such stuff is exceedingly rare. When they do happen then its probably because someone is being a complete idiot.