"...Shouldn't evidence of that tsunami still be present in modern England and Scotland?
Has erosion altered the landscape that much in 8100 years to erase all evidence of deposits?..."
Sea level may have been lower then...some of the evidence (scouring, erosion scars, etc) may be underwater at present.
I did a short paper on my interpretation, as a marine navigator, of a Spanish ship wreck on the Oregon Coast.
Old charted anchor bearings did not match the waters of the bay until I matched what the bay was supposed to look like 500 years earlier. Thanks for the info from Oregon State University Hatfield Marine Science Center.