I agree that the Houghton pheasant isn't pure, but are they Wolferton birds not pure too? I'm yet to see any convincing evidence that this is the case, though I'd love to hear from anyone who can supply this.
The Wolferton birds belong to the dark-throated form '
obscurus' which is a variant that seems to occur in captive and small feral populations. It is often mooted that it arises from hybridisation but I think it's also possible that it occurs as a result of inbreeding. Allegedly the Wolferton pheasants never used to have dark throats (though I would welcome proof of that - could it be that people just weren't alert to it and looking for it?). If that's true, and they acquired the dark throats through hybridisation, then it's surprising that no pure Lady A's or first generation hybrids have been seen in the area (unless they have, but I've not found any reference to them if so, and certainly not seen them myself). Of course it's possible that impure birds were released in the area after a population of pure birds was already established, and that these have now infiltrated the whole population, but I suspect not. In-breeding is likely to occur in captive populations as well as tiny feral populations, and is likely to create mutations, so it is not surprising that a recognised mutation might occur within the dwindling Wolferton population without any hybridisation taking place. If this is correct then as the Breckland population declines we might expect to see the same thing happening there, and sure enough the last Golden Pheasant I saw in the Norfolk Brecks a couple of years ago did indeed have a dark throat, albeit not as dark as on the Wolferton birds.
A few photos of dark-throated and normal
Golden Pheasants here if anyone's interested.