This is a nice map from the 2011 BGS Research Report, showing the accepted Devensian ice limits for South Wales at the time of publication. Things have changed -- the Swansea geomorphologists now think that the whole of Gower may well have been affected by glacier ice at the time of the LGM, and the ice limit shown off the Pembrokeshire coast has to be wrong; if the Devensian Irish Sea Glacier was powerful enough to reach the Isles of Scilly, it must certainly have pushed far up into the Bristol Channel as well. Also, there is fresh till on the south side of Milford Haven at West Angle and on Caldey Island, so the line as shown is at least 20 km away from its actual position....
Anyway, it's a nice map, showing the deep depression of the Somerset Levels. You need to take the coastline on this map as approximate +120m contour at the time of the LGM, since sea level was a great deal lower around 20,000 years ago.
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