It's not hard to imagine that the dragon had something to do with it -- hence the pub name.
But I think TTT effectively *has* explained why St. George is England's saint -- it's Edward III's "fault". Before then it was Edward the Confessor and/or St. Edmund, who were both actually English.
well the reason is not specifically stated but St George became a Christian and refused to budge despite a lot of Torture, he was finally beheaded. His head is in a Church in Rome. Perhaps Edward III much admired his stoicism.
Also the Dragon was often used to portray the devil and St George being a good christian is portrayed slaying evil. There are accounts of George as the Roman officer defending villages etc of the excesses of other parts of the Roman Army at the time. He lived around 3rd century AD and no doubt impressed Edward some 1700 years later.