The most important thing for any De-Ac weapon is the proof mark stamped on each major piece. This is bolt, frame and barrel. The mark will be two crossed swords, with the letters DA ,and a date. The position of the letters will indicate which proof house London or Birmingham. If these are NOT present, regardless of how many bits of paper or what's been done, the weapon is dubious. There are some very early de-ac's that do not need proof marks. But it would take a lot of study, not nesacarirly under the best of circumstances , to prove the point You say your's are modern de-ac? The marks should be there. They may be dispalyed, but be sure there is a good reason, such as a show or parade. For purposes of transportation treat as real, the trigger MUST be covered, but better to get a couple of cheap slips and cover the lot. Apply common sense. As for the 'criminal' side of it. The aggrivating factors for any crime are 'Take the W.I.F.E.'. Weapon, Imitation firearm, Firearm, Explosive'. a de-ac would fit at least two of those!
The 'act' you talk of do you mean the V.C.R.? That would make it illegal to own, manufacture,import or display a picece of wood shaped as a realistic firearm, with certain exceptions, but NOT a real De-Activated weapon! Go figure, we can't.