Hi, Thank you everyone for your help.
Milly has found John Connell O'Brien,he's the one born in Islington in 1873. A relative has his baptism record.[He was Catholic.]
Looking again at his papers,and yes they are Militia, the term of testament could well be six.
As for the questions about his wife Mary,she came to England to look for work[or for John?] but as I said she married again in 1905.When her sons from marriage one came knocking,she turned them away. Her younger son was my grandad and he never spoke of his mother,even though he married his cousin,the daughter of his mothers sister.
I still have found no trace of John after his marriage.