It would be fortunate to find her marriage in Ceylon. Parts of Norman’s family, in particular the Cantlays (Norman’s sister Laura Rose married in Colombo in 1877 James Cantlay) settled in Western Australia. But you say that you have searched WA marriages.
None of Norman or his siblings’ births or baptisms has ever been found other than their sister Frances Ellen Hampton who was born in London on 30 Mar 1866 and baptised at St John the Evangelist Notting Hill on 11 May 1866. Frances married into another Anglo-Ceylonese family named Rudd and lived there with her family, died in Kandy in 1946.
Josephine M Hampton in Sussex is the only Josephine in the 1939 Register who fits. For her to be actually “Josephine Marion”, allied to a birth within a reasonable time frame adds to that probability. Other records such as electoral registers do not show birth years. There are other Josephine M Hamptons but no way of telling. I think the only way to confirm or rule out this Josephine would be for her to have had children who could supply DNA, but no indication of children?
It is not unheard of for persons to advance their birth year, and Josephine was so much younger than Norman.
A word of caution surrounds the person “Norman Augustus” Hampton who is listed in some trees. While the Josephine we are concentrating on is in Sussex, at the same time in Surrey is a Norman Augustus Hampton, living in Caterham Surrey with Gwendoline Molly Hampton, along with Eva and Sarah Edwards. A Norman A Hampton married at Godstone in Surrey in 1933 Gwendoline M E Edwards. So I think I can say that the Norman Augustus Hampton shown in at least one on-line tree is not Norman A Hampton from Ceylon born 1871. (To complicate that, Norman had a 2nd cousin named Gwendoline Molly Hampton Lewis, from part of the family that never went to Ceylon.)
If I were to take a stab at Norman’s middle name, in the absence of anything otherwise compelling, Norman had an older brother named Arthur, who was unmarried in 1891, born Ceylon, working in a London bank aged 31. I think he went to South Africa. I can see no forebear with the name Arthur however.
So, no closer to finding that marriage. But thank you for reviving my search for more about this family. By the way, Norman’s brother Joseph married, for the 2nd time, Emily Hill Gardiner 1900 in Colombo. She originated in Old Aberdeen where her father had been the Rev’d Thomas Gardiner. This puts them closer to your location.