The British are known culturally for many things, one of them “reserve”. Reserve relates to the general disinclination to show emotion, feelings or to act in any way that could be viewed as slightly off-centre. The cultural concept heavily correlated with the sense of privacy the British hold.
As a result of British reserve you will note that language is heavily tempered and gestures are restrained. Neutrality and diplomacy in communication are seen as necessary components of courtesy. British reserve does not mean that Brits are boring, lifeless and unemotional. It simply means that in British society people are trained from school-age to be self-contained and not to be open emotionally.