Sorry Milky400, didn't mean to ruin anyone else's experience with the last post. If anything it was a nice touch from the folks as LR.
The letter that came in the box says "they're constructed of the very latest in ABS plastic technology with a specially engineered washer in the head of the cap"
Not certain but I reckon the ones sold as options are of the same construction, if you spec them you'd get either the black/white union jack or colour union jack on the car ("price includes dealer fitting"!). I imagine you'd also get the LR design ones in the post like everyone else.