Weird white thread at selvedge - MOD RRS tartan

[Tobus]

I recently purchased 10 metres of what was advertised as MOD surplus Royal Regiment of Scotland tartan, double-width. I didn't notice it in the seller's photos, but when it showed up I immediately noticed a prominent white yarn at the selvedges. I've discussed this with a few people elsewhere, and the consensus seems to be that it's strange. I cannot find any online photos of any RRS kilts that have this at the bottom.

Has anyone here seen this before? It was suggested by figheadair that it could be a guide thread for the tuck selvedge. I'm wondering if it could be removed safely (perhaps by snipping it every few inches and pulling it out) without degrading the integrity of the selvedge. And on that note, I have to say that the selvedge looks pretty rough. As you can see below, the weft threads loop pretty far out past the edge, and very unevenly. It seems to be worse in the green fields. Between the quality of the selvedge and the silly white thread, I would be very hesitant to go to the expense of having a kilt made from this. I'm actually wondering if this material was rejected by the MOD, which is why it got sold off as "surplus" and at a bargain-basement price. Aside from that, it seems like pretty good heavy tartan.

So, kiltmakers and others who handle a lot of tartan including government stuff, what are your thoughts? Have you ever seen government-spec tartan with this odd thread?