I think based on the information Graham you are right when you say your a little old fashioned
I dont know if Kesters g/f is already married or if he might rather live with her for a while longer and register a civil partnership,and seek settlement that way,or indeed if they will ever have a child.
Any issue will have the right to a UK passport as long as he is on the Birthcertificate and can as a British Subject call themselves by whatever name they choose.
Not everyone believes or needs the institution of marriage although it may make dealings with the authorities easier
