[mothered]

in places it says that the receiver can claim if the item arrives damaged. It doesn't mention anything (or from what I can see) about a parcel arriving without its contents.

Just because It doesn't mention missing Items on receipt, It doesn't mean they won't compensate for such Items.

They may well have purposely excluded that- just to minimize the number of claims for goods that never arrived. Of all SE's I've performed, seldom have I come across a company that (upon "seemingly" solidifying my claim that the package was tampered with In transit), rejected It altogether.

The item weighs next to nothing so this isn't an issue, it is making the envelope look like it has been tampered with, because they can't accept them if they have been ripped

Do they actually state that they don't accept damaged packages?

Yeah, they do.

After thinking about this and what it will entail, I'm going to just send it.  I'm trying to quit smoking anyway so maybe this will help me on a bit lol.

It would be a good experiment though to see if the Royal Mail are vulnerable.  I may try it in the future, it could prove to be a good method.

By sending It off, you have nothing to lose and everything to gain.

It's a little harsh on their end not to accept damaged packages. Looking at It from a legit standpoint, you've sent the Item In good faith and was tampered with during transit. I don't see how an Item that was dispatched In It's proper form, Is not accepted due to something beyond your control.
Once you send It, It'll be Interesting to see the process on their end and ultimately the outcome.