The ending of the Roman occupation was Britain’s first Brexit, which probably happened about AD 408-409.
That’s when the experience of being part of the Roman Empire finished in Britain.
In the latter 4th Century more and more field army troops were being taken from Britain to the continent by the various usurpers. Ultimately, Constantine the Third usurped in AD 406-407, and when he took the final field army to the continent, they never came back.
Therefore, the Romano-British aristocrats between AD 408 and 409 realised they were getting no ‘bang for the buck’ in terms of the taxes that they were paying to Rome. So they threw out the Roman tax collectors, and this is the schism: this is the ending of Roman Britain.
However, the way that Britain left the Roman Empire at that point is so different to the way that the rest of the Western Empire finishes, that it cements in place Britain as a place of ‘difference’.
How was Roman Britain’s experience different to continental Europe’s?
So this was Britain’s first Brexit, and the way that Britain left the Roman Empire during that period was very different from the rest of the continent when the empire collapsed later in the AD 450s, 460s, and 470s.
This is because the Germans and the Goths who took over from the Roman aristocrats, the elites, as the empire in the West collapsed knew the Roman ways. They came from immediately around the Rhine and the Danube. Many of their soldiers had served in the Roman Army for 200 years.
Later Roman generals (magister militum), were Germans and Goths. So they simply took over the very top level of society, but kept all the Roman structures in place.
Think Frankish Germany and France, think Visigothic Spain, think Vandal Africa, think Ostrogothic Italy. All you have happening here is the elites being replaced by these new incoming elites, but the rest of Roman society structure stayed in place.
This is why to this very day, they speak languages often based on Latin languages. This is why the Catholic church predominates in many of these regions to this very day, or until the modern era certainly did so. This is why the Law Codes in many of these regions are based on originally Roman Law Codes.
So, basically, Roman society in one way, shape, or form has continued almost to this very day.
Britain after Rome
However, in Britain, the experience is very different. From the later 4th, into the early 5th centuries the East Coast was been increasingly predated by Germanic Raiders; the Anglo-Saxons and Jutes from popular legend.
Therefore, a lot of the elites who could afford to leave actually did leave and a lot of them left for the west of Britain.
Lots of them also left for the Armorican Peninsula, which became known as Brittany because of the British settlers there.
So there wasn’t much of Roman society structure left for anybody coming in to actually take over, especially on the east coast.
More importantly, the Germans who came over and then stayed, the Germanic Raiders, weren’t Goths or Germans from immediately around the Rhine or Danube. They were from the very far north of Germany: Frisia, Saxony, the Jutland Peninsula, Southern Scandinavia, so far north that they didn’t really know the Roman ways.
So they arrived and found nothing or little to take over. Even if there had been Roman societal structures for them to take over, they didn’t know how to do it.
That’s why today we’re talking in a German language, not a Latin language. That is why the law codes of Britain today, for example, the common law are evolved from Germanic law codes. It all dates back to the experience of Britain leaving the Roman Empire.
And then you have a couple of hundred years of the scouring from the east to the west of this Germanic culture. It gradually replaced the Romano-British culture, until the kingdoms in the southwest of Britain fell.
Ultimately, 200 years later, you have in place the great Germanic Kingdoms in Britain. You have Northumbria, Mercia, Wessex, East Anglia. And the Roman experience in Britain has been wiped clean, but that is not the case on the continent.