There are some very out of date maps and theories circulating about the extent of the glaciers of the ice ages, much of it sadly spread by Stonehenge conspiracy theorists. It isn't hard to make sure only the latest and best information is used as the basis for any discussion. Here are a couple of pointers.
The Devensian British-Irish Ice Sheet
The Devensian British-Irish Ice Sheet was a large mass of ice that covered approximately two thirds of Britain and Ireland around 27,000 years ago. All of Scotland and Ireland, most of Wales, and most of the north of England was underneath the ice sheet during the Last Glacial Maximum. This ice sheet retreated and shrank after 27,000 years ago, and had completely disappeared by 11,300 years ago
For a recent comprehensive review: Chiverrell, R.C. and Thomas, G.S.P. (2010), Extent and timing of the Last Glacial Maximum (LGM) in Britain and Ireland: a review. J. Quaternary Sci., 25: 535-549. https://doi.org/10.1002/jqs.1404
And for the very latest including information about the Welsh Ice Cap and the Preseli Hills please see this chapter:
Philip D. Hughes, Chris D. Clark, Philip L. Gibbard, Neil F. Glasser, Matt D. Tomkins, Chapter 53 - Britain and Ireland: glacial landforms from the Last Glacial Maximum, Editor(s): David Palacios, Philip D. Hughes, José M. García-Ruiz, Nuria Andrés, European Glacial Landscapes, Elsevier, 2022, Pages 407-416, ISBN 9780128234983, https://doi.org/10.1016/B978-0-12-823498-3.00033-9. (https://www.sciencedirect.com/science/article/pii/B9780128234983000339)