The Holocene Storegga submarine slide occurred on the continental margin off western Norway about 8000 calendar years BP, causing a tsunami which is known to have reached coastlines in Norway, possibly Iceland, the Faroes and the UK (mainly Scotland). The UK evidence consists of largely comparable deposits from 33 sites, involving 47 radiocarbon dates with pollen, diatom and particle size determinations. An age of around 7000-7100 radiocarbon years BP or 7800-8000 calendar years BP for the event is preferred. the magnitude was considerable. Run-up of the tsunami of over 5m and probably several metres above that is inferred from the altitude of the sediment and its particle size characteristics. At least two waves are indicated by the particle size graphs. The impact involved erosion of dune and shingle barriers at several locations and widespread inundation inland. Using altitudes obtained on the shoreline reached at the time of the tsunami, a new isobase map of Scotland is shown, using a statistical technique new to sea level studies.