A few further titbits. I have had a look at Griffiths Valuation, printed around 1857/1858, and there are 13 Winterscale entries. Nine of these are for properties in Old Mail Coach Road and Pound Street, Knocknaganny, St Johns Parish, County Sligo, where the landlord is in each case Elizabeth Winterscale. St Johns Parish is I think the parish which covers Sligo Town. I would guess that this is Elizabeth Winterscale, the mother of John Winterscale, although I believe from his will that she died sometime between 1850 and 1857.
There is then a single entry for a property in Knappagh Beg, again in St Johns Parish, which shows the landlord as Eliza Winterscale, which may be the spinster sister of John Winterscale mentioned in his will. But then again, Eliza and Elizabeth are pretty inter-changeable, so it could be the same person.
The other three entries are for Richard and Patrick Winterscale in Cloondeash, Ballyhean Parish, County Mayo, away to the west of Sligo.
The other interesting thing I have come across is an entry in Pigot's directory of Ireland for 1824, which shows 'James Winterscale, Esq, Sligo' as one of 24 Commissioners for the Improvement of the Town and Bay of Sligo. This I take to be the father of John Winterscale, noted on his death certificate in 1858 as deceased and having been a London proprietor.
Linking this information with what is said in John Winterscale's will, I am beginning to wonder whether John was the only son of James and Elizabeth Winterscale, and that he had just the two sisters, Mary (Davis/Davys) and the spinster Eliza. If so then the name Winterscale would only be carried down in this family through John's only son John Francis Mair Winterscale, who married and lived most of his life in England (in Bristol/Dwevon/Wiltshire).