“Scientists have warned that Britain’s coastal areas and infrastructure are under threat from tsunamis.
New research has revealed how the British Isles have been hit by giant waves at a much higher and intense frequency that previously believed.
One tsunami reached more than 60ft in height, with warnings that the waves could devastate coastal installations such as power stations and shipping ports.”
The illustrative map shows the vulnerable areas include the Hinkley nuclear plants.
East Devon Watch 
Even more to the point, there was exceptional flooding possibly resulting from a tsunami in the Bristol Channel in 1607: https://en.wikipedia.org/wiki/Bristol_Channel_floods,_1607
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