There is indeed good evidence that glacier ice reached Somerset from the west. There are many studies in the literature. The ice came from the west. How far into Somerset is came is another question -- my preference is for a glacier edge somewhere near Glastonbury, but others think the glacier extended all the way to Salisbury plain. Have a look at this fantastic modelling reconstruction of the Last Glacial episode:

http://qra.org.uk/British_Irish_animation.wmv

Since it is now known that the ice reached the Scilly Isles around 20,000 years ago, all the laws of ice physics mean that it must also have transgressed well into SW England at the same time. Watch this space....