214 Roman Britain was divided into two provinces

... Britannia Superior and Britannia Inferior, with administrative centres at London and York respectively.

Sometime after 305, Britannia was further divided, and made into an imperial diocese. For much of the later period of the Roman occupation, Britannia was subject to barbarian invasions and often came under the control of imperial usurpers and pretenders to the Roman Emperorship. Roman officials departed from Britain around the year 410, which began the sub-Roman period, but the legacy of the Roman Empire was felt for centuries in Britain.