Marvel Comic's Captain Britain, A.K.A Brittanic, A.K.A. Brian Braddock is probably the U.K.'s best known superhero. I say that because I'm in the states and I've heard of him. Created by Chris Claremont and Herb Trimpe, Captain Britain made his first appearance in Captain Britain Weekly #1 in October, 1976. Designed to uphold the laws of Britain, Captain Britain was meant to be the U.K. version of Captain America.
Brian was born and raised in the small town of Maldon, Essex and educated at Fettes College in Edinburg. He was a shy and studious youth, living a relatively quiet life and spending a lot of time with his parents and siblings.
After his parents were killed in a laboratory accident, Brian took a fellowship at Darkmoor nuclear research centre. When the facility is attacked by the technological criminal Joshua Stragg (A.K.A. "The Reaver"), Brian tries to find help by escaping on his motorcycle. Although he crashes his bike in a nearly fatal accident, Merlyn and his daughter, the Omniversal Guardian, Roma appear to the badly injured Brian. They give him the chance to be the superhero Captain Britain. He is offered a choice: the Amulet of Right or the Sword of Might. Considering himself to be no warrior and unsuited for the challenge, he rejects the Sword and chooses the Amulet. This choice transforms Brian Braddock into Captain Britain.
Brian is superhumanly strong, able to lift 90 tons, and possesses enhanced reflexes, stamina and senses. He can also fly up to 770 mph for prolonged periods. He derives his energies from the friction between dimensions, focused in a matrix centered on the U.K., and formerly needed his costume to focus his powers and provide a battery when outside the U.K.; however he may have alleviated this weakness when he briefly severed his mystic connection to the U.K. to empower Kelsey Leigh. As Britannic, he had prophetic visions, tied to memories of experiencing all history while lost in the timeline. He is apparently immune to his sister's psionic powers, though not his elder brother's reality warping abilities.
MI-13, the Corps, agents of Merlin, champions of Otherworld's Camelot, Pendragons, and Hellfire Club.
You can find more information, as well as a detailed history of Captain Britain HERE at Marvel.com!