This idea came up quite a few years ago but appears to have been rejected by most scientists as unlikely. Smacks of catastrophism I suppose – but in this instance all it would take is the collapse of ground on the continental shelf around Britain as a result of an earthquake. The researchers seem to be having a second go – see https://phys.org/news/2026-01-tsunami-bristol-channel-centuries-revisiting.html … It is essentially a revisit of the AD1607 flood wave that bored up the Bristol Channel and caused widespread damage and loss of life – on both sides of he Severn estuary. It primarily affected people living in low lying areas – such as the Somerset Levels, or coastal marsh and field. On January 30th 1607, on a calm day with a bright sky, the sea rose up without warning. The wave raced inland, tearing across fields and swamping villages, destroying homes and drowning livestock. People were washed away and the numbers are not recorded. There was an estimate. At the end of the day thousands of acres were under water and around two thousand people are thought to have died. Bear in mind the low population density in the 17th century. What caused it?
The sea water affected communities in South Wales, Somerset, Gloucestershire, and Devon – inundating some areas several miles inland. The rising water is described in one source as huge, mighty hills of water tumbling over one another. It occurred at 09.00am in the morning amidst what is described as fair weather. This is not at all like a storm surge but is akin to to eyewitness accounts of tsunami waves in other parts of the world. The researchers went on to identify a suite of features with a chronological link to the 17th century. For example, a sudden erosion of two spurs of land that had formerly jutted out into the estuary. They disappeared. The nature of salt marsh deposits and layers of sand in otherwise muddy sediment. There is also the movement of large boulders along the shoreline. I suspect the argument for or against will persist for a long time.