Yes 3 stories in all I believe contained in the three books below together with several other well known authors who contributed stories as well, however I don't unfortunately know the titles of them. Go into the Society's website by clicking on the left of the bar across the top of this page, then into Internet Archives - clicking on the red cross top right to remove the banner - then click on Winston Graham. Finally click on Bibliography, where all his known works are listed, and scroll to the bottom where there are these three listed together with some general notes.
1. The 7th Fontana Book of Great Horror Stories - 1972 2. Realms of Darkness - 1985 3. The Mammoth Book of Twentieth Century Ghost Stories - 1998
Hope this helps....
"Perfection is a full stop .... Ever the climbing but never the attaining Of the mountain top." W.G.