There are plenty of RFDs who do not have the knowledge to competently adjust the power of every airgun taken in to them. In that case they would have to keep the gun until you'd applied for a license, or pass it to another RFD for repair. If you couldn't afford the charges for the work required or couldn't get an FAC then it would seem to you like your gun had been "confiscated."

The only real difference would be that the gun would remain your legal property until you had managed to make some kind of arrangement with the RFD. If you got arsey about it the RFD would be within their right to report you for possession of an illegal firearm, since you did possess it immediately before handing it to them.

It sounds like you own your own chrono...