Some romans would state picts and britons and more exotic names were used. 449 CE<quoted text> Not really correct. The kingdoms were not formerly known as Uk or Britain, it was after the unity that they became known as that. The people of England were solely known as the English to date, even if they are united under the umbrella of Britain Or British.
It took till about 550 CE until the Angels, Saxons and Jute had some real foothold.
Using the name Brits would be going back to a former idea of unity, since that in fact never really happened. But this kind of souvereignity is a source of pride.
The lingo used now was as far as i know invented by BBC radio.