I see the concept of Britishness as an artificial identity created to dillute and eventually replace English identity. The concept of Britishness was created to benefit the royals and the elite, it works against the native English. It also significantly furthers the mass immigration agenda as anyone can be "British", whereas only native English people can really be English.
In fact, for the most part it's only English people who even identify as British. Most Scottish, Welsh and NI people do not, some may claim to when it suits them, but generally they will always identify first and foremost as Scottish, Welsh or Ulster/Irish. Most of them do not feel strongly British at all, and if a foreigner claimed they were "British" I have no doubt that most of them would quickly correct them.