At https://eurekalert.org/pub_releases/2018-09/uop-gra091218.php … the British mainland, we are told, was formed by the collisions of three land masses. It has long been thought that most of Scotland was not always part of the British Isles – but now geologists have been investigating the SW of England and have come to the conclusion there was a third piece of the puzzle. This concerns all of Cornwall and a large dollop of Devon. They say this piece of real estate was once part of France (pointing at similar geology in Brittany) and separate from the rest of England and Wales. The study in Nature Communications (Sept 2018) says this occurred some 400 million years ago.
The idea revolves around mineral properties and rock features across Devon and Cornwall. Rocks and landscape north of the boundary have an affinity with the rest of England but south of it the connections are with France. They say this may explain the abundance of tin and tungsten in the far SW and the lack of it in other parts of Britain. Tin and tungsten are also a feature of the geology of Britanny,
Apparently, this is a completely new way of thinking about how Britain was formed. Field research was done at 22 sites in the SW (along the proposed boundary) but no doubt modelling was involved prior and after the field research. The boundary ran from the Exe estuary and Camelford in the east. It ran across the top of Dartmoor for example, with its ancient granites. This is an interesting idea as it could encompass the granite or magma outcrop that runs like a spine from Dartmoor to Lands End and includes the Scilly Islands (most of which is now submerged). This has been deduced to occur because the spine slopes downwards from Dartmoor out into the Atlantic. At some point the geology was alatered by tectonic activity – or perhaps because the geoid of the earth has changed. The idea doesn't seem to contradict the way the geology is currently perceived although the idea land masses were mobile prior to Pangea is a hypothesis and may not strictly be as the theory allows.
The same story can be seen at https://phys.org/print456116832.html .. which also has an image of Scotland (virtually to the borders) as part of Laurentia – a different land mass to England and Wales.