Personally, I think you might be on shaky ground unless you are UKARA registered, because when you put sticky camo tape over it, you were technically making it potentially more realistic-looking, and the law is very specific about the act of doing that being classed as 'manufacturing' 'a realistic appearance'. That is fine if you are registered and using it for airsofting at a UKARA site and transporting it in a case or the boot of your car, but otherwise, then it is most definitely contravening the law.
Essentially the CPS will see it like this: In removing the tape, and as a result, the paint, it was not an accident that the paint came off, but occurred as a result of an attempt to make the thing look more convincingly realistic. This is as opposed to it simply wearing off, which would be more arguable as a defence.
Of course if you are using it for skirmishing and have a UKARA registration, then it's no big deal, but if you are not using it at a UKARA site, and perhaps going in the woods or fields to have a battle with some friends or some such, then the gun is supposed to be easily distinguishable from a real firearm. This is for your protection more than anyone else, since if an armed response unit shows up, they might well shoot first and ask questions later, and you couldn't really blame them for doing so if they thought someone had an MP5 that was camo'd up.
