I don't really see what the problem is with getting a "pre christmas" xbox.
Just have a look on ebay, it is getting flooded with them and cores are going for way under £300. I purchased mine last night (feedback of about 3000 so no probs there) for £250 + £20 delivery. The cheapest "game" in manchester here did the core for on launch day was £350 (including extras i didn't want) and that was preorders only!!!!
£270 is really not bad value when you consider they are £209 retail. Just get a HD for christmas off the family and you're laughing.