think about it the other way... if you have a gun that's doing 30, and just needs an allen key to get it under 12, then you can perhaps understand that if that situation arose where a gun was deliberately setup to do so, that the police might like to explore that to get a conviction. Not saying that's what's happened here, just that i'd expect more pressing weight in the testing in that situation than perhaps a target shooter who's gun was sold as 12, hasn't been deliberatly modded to go over, being tested... if you catch my drift.
You have to take a bit of faith that a lot of the time, guns don't just get some random testing to a hard degree for the fun of it. Normally there's a situation that has arisen, or background information that leads the police to suspect something other than may be apparent.
I would think that a gun that isn't readily wound up to non legal power or that isn't designed to do so, that hasn't been confiscated due to other circumstances might find itself not undergoing such rigourous testing. The police generally are interested in serious crime rather than chasing pcp owners around all day. I think the question you should ask is why would the police ever think you would have something to gain in winding up a gun for the possibility of it being illegal, if that's even possible. Your a target shooter, it has no benefit, you can't shoot competition with it, you don't hunt with it, it's not likely your going to go for some long range poaching session with a target rifle. Slap a load of camo and hunting gear in the bag, and with something that is capable of well in excess of 12, get caught driving around the middle of nowhere at 3am, and the story may be different... catch my drift?
Stay legal, stay sensible, stay away from being close to the limit, follow the sport responsibly and i doubt you have anything to fear. If you can make it difficult for you to even adjust it, then I think that's all you can do.
We must remind ourselves that as much as some esoteric methods can drive a rifle over the limit, the manufacturers and sport bodies and those that participate have no interest in doing so. There really is no point. We have chronos on competitions not for legality reasons (because they're not a forensic device), but just to ensure an even playing field, and perhaps to remind people who may fettle that they need to ensure they're within competition limits, which are inside the legal limits.
The only time i've been interviewed by police was when I was walking through central london after some nubar had been shooting at buses with an air rifle. Being smart I had ID, club ID, was more than polite and cooperative and there was no problem.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep