When writing
Cool Britannia, Adam and I came across a lot of literature on the Pennines and the Lake District. Cross Fell had more written about it than just about any other hill in northern England. What we discovered was that, although doubtlessly more snow used to fall in the period the book covers, snow has never been known to persist in England until the following winter. The latest month we have reliable reports for is August. In 1979 a local farmer at Temple Sowerby reported two tiny patches at the head of
Crowdundle Beck on the 18th of August.
I think that it is entirely plausible, though, that snow has persisted in exceptional years on Cross Fell during the Little Ice Age. The topography of the hills favours long snow lie, as opposed to the sharp and craggy hills of the Lake District. Unfortunately, however, there is no concrete proof of it having happened.
The longest-lying patch of snow in Wales is
generally to be found at
Y Ffoes Ddyfn (the deep cut) on Carnedd Llewelyn. This patch has been observed for a good many years, though sporadically. An account of James Orchard Haliwell from 1860 talks about snow on that mountain persisting until 'the close of August'. In 2010 the snow there persisted until June 28th.
I can thoroughly recommend Cool Britannia to you and your friend...