Thank you all for your comments, help and replies.
Liz, thank you for your continued help in this, you have looked for a marriage for WHC for me but there doesn't appear to be one from the Isle of Man. I don't know if you saw the WDYTYA that I referred to and also Mary mentioned it. It is a classic case of one partner finding another life and partner but still being married to another. With Helen/Ellen Fanny Cox stating herself as a widow in Islington Middlesex on the 1901 census I feel that she either didn't know what happened to him or she just 'wanted to wash her hair' of him and said "I have no husband I am a widow".
Regarding the subject of Sheffield ............ as mentioned one of the candidates for WHC as a young lad, was on the 1841 with his parents and siblings in Birmingham, on the 1851 the family moved to Sheffield William Cox aged 17 was a silver plater, on the 1861 his parents lived alone still in Sheffield. So regarding the newspaper article that a William Henry Cox aged 77 was from Sheffield, perhaps he referred to Sheffield as where he hailed from. Also a partner may not have necessarily known where their partner came from, especially after a short time together and WHC may have just talked of a life in Sheffield, not mentioning Birmingham, Devon or Sussex.
As a recap I have added my message from the evening of Saturday 22 August as that was one of my latest messages.
Thank you Liz for your time and help.
To be honest not knowing the Isle of Man I have no idea how big a search for William Henry Cox would be. Basically I need to know the earliest that he can be found in voters books anywhere on the island, to find out when he is first recorded on the Isle of Man, (it would be from 1891) if you can help with this at all, however small it would be much appreciated. You have searched the Douglas ones from 1900 to 1906 with no trace so perhaps he was lurking on another part of the island! The entry from 1899 Union Mills is most interesting to me, as you say there was another name, would you be able to check this one out for me to see what the middle name was and also the ?? bit after the name Cox, that you mention.
Thank you again.
Ewan
ps
Liz, I don't know your email address, you can always send a private message on roots if you want.
Many thanks
Ewan