By the early 5th century, the Roman Empire could no longer defend itself against either internal rebellion or the external threat posed by Germanic tribes expanding in Western Europe. This situation and its consequences governed the eventual permanent detachment of Britain from the rest of the Empire. After a period of local self-rule the Anglo-Saxons came to southern England in the 440s.

The end of Roman rule in Britain was the transition from Roman Britain to post-Roman Britain. Roman rule ended in different parts of Britain at different times, and under different circumstances.

In 383, the usurper Magnus Maximus withdrew troops from northern and western Britain, probably leaving local warlords in charge. Around 410, the Romano-British expelled the magistrates of the usurper Constantine III. He had previously stripped the Roman garrison from Britain and taken it to Gaul in response to the Crossing of the Rhine in late 406, leaving the island a victim to barbarian attacks. Roman Emperor Honorius replied to a request for assistance with the Rescript of Honorius, telling the Roman cities to see to their own defence, a tacit acceptance of temporary British self-government. Honorius was fighting a large-scale war in Italy against the Visigoths under their leader Alaric, with Rome itself under siege. No forces could be spared to protect distant Britain. Though it is likely that Honorius expected to regain control over the provinces soon, by the mid-6th century Procopius recognised that Roman control of Britannia was entirely lost.