A flashlight or two is probably prudent. Ibuprofren, Tylenol, and an antacid/antigas medicine are an imperative on long flights. If your plane should fall down crossing the north Atlantic, I would think that there's really nothing you can reasonably take with you that would mitigate that sort of exposure.

As far as the Brits go, the enforcement of their tote laws is so interpreted that I would not carry any knife unconcealed in public. Maybe out in the countryside, but I just don't trust the bobbies judgement.