If I compare the British with citizens of other European countries I have worked or lived in the British are still shy of displaying emotions in public. Parents tend not to hug or kiss their children in public, except babies.
Politics are a major topic of conversation to the British, whereas in Scandinavia, Germany, the Netherlands and Spain you discuss politics with old friends or family, but not with more casual acquaintances or at a friend's for dinner. There you discuss books, films, the theatre or other cultural issues.
Scandinavians are always surprised by how little the British say thank you! Here we thank each other continually for meals, visits, outings, coffee, ice cream not only when food or drink is offered but before you part. Visitors are expected to say thank you for a lovely time, the next time they meet their hosts, even if the host is a sister or brother and not only on the way out of the door at the end of the evening.
You are also expected not only to wish the birthday boy or girl a happy birthday, but to congratulate the parents as well, or in the case of grown-ups the spouse. You are also expected to congratulate the parents as well as the child who has passed an exam.
None of this is considered necessary in Britain.
No Polish child or French either would dream of addressing an adult by their given name. A German child might just, but would not be surprised at being corrected for doing so and would still be expected to use the formal pronoun to an adult who is not a near relation.
So politeness as such is not a British trait, but the form it takes can well be.
Basically, the outside world equates London manners with Britain because they do not know that Welsh, Irish, Scottish and Northern English people do things differently.