As a Brit , i personally think the secrets are in the genes, the cold temper sort of accounts for most far Northern European people ie Scandinavians, Dutch, Germans,etc anything above France basically.
I can see it first hand, I have two young sons by my Argentine wife who is Italian decent. One of my kids is darker skinned, has a terrible temper and cant lower his voice below max volume most of the time. He also has no sense of others personal space (joke!). Anyway, Hes the Latino. My other son is blonde , blue eyed, no temper, sweet natured and generous , if he has 2 sweets, he`ll give you one if you ask. Hes the British one and people say that here.
But alot has to do with up bringing of the mid-upper classes in Britain that are taught to have good manners, respectful of others and polite. Its just some of the lower classes and politicians that are general arseholes in Britain. I noticed that my in-laws here never teach my sons to say please/por favor, thank you/gracias, etc. Where as i`m always correcting them if they dont say those words. Maybe theyre just laid back about it and i`m the strict one. But i hope they turn out the better for it.