I know I’ve said this before, but the subject keeps coming up.
If you ask the police about a sgian, they will tell you what the applicable law is. HOWEVER police (at least in the U.S.) have a fair amount of discretion.
In my jurisdiction, a fixed bladed knife of any length is unlawful. But if you are kilted with a sgian sticking out of the top of your hose, I would not expect an officer to give you any grief about it.
Granted, if you’re drunk, harassing people, hanging out in a drug area, or otherwise being a public nuisance, then I would expect the officer to view your sgian as a weapon – and take appropriate action.

Now I realize that some jurisdictions – and even some individual officers – are more Draconian than others. Even so, I cannot believe that keeping a sgian in your own home, or only wearing it to formal functions would run you afoul of the authorities.

Derek, I’m truly sorry your blade was neutered, but I’m glad you found a way to salvage part of it in a way you can feel more comfortable about.
Personally, I’m with David – I will be happy to help find a home for wayward sgian dubhs.