My great grandmother's married name was Kidd (husband Charles Forbes Kidd). My grandfather William was born in 1886, which would have made your Isalen Jane 38 years of age at his birth. Possible but unlikely. However, all of the other Jane's that have been suggested to me do not seem to have the right sort of background- Isalen Jane does.
All I know is that in 1911, at the time of my grandfather's marriage, Charles Forbes Kidd is mentioned on the marriage certificate as being a (hansom) cab driver from Streatham Vale, London.
Both Charles and Jane are proving to be particularly elusive and I have been unable to trace any records of them with any certainty from any part of the country. I have a vague memory of being told that Charles was from Scotland but that is the limit of my knowledge so far.
I will keep on trying though and a big thank you to everybody who has contributed to this thread.