Joe, this post posed a question about what will the British Consulate accept.
Thus I was answering that question. Sorry to pedantic.
If one just wants to know for a private reason, then its up to that person to decide who's word they can accept; whether a particular lab is trustworthy and competent, and what they are hoping to establish.
If a couple just want to know who the parents are, i.e the father or maybe to ensure there was no mix up in the hospital with the babies, then providing the interested parties are present when the samples are taken and sealed and posted, I would assume that would be sufficient.
But as I said, this was a specific question about what the Consulate would accept.
Although I could not say what that would be for certain (although September did say only St Lukes) I was reasonably confident that, for the reasons I explained, a postal test would be insufficient as it would be too easy to fiddle it.