Hi Natalie
I’ve looked at several sets of records for all the people you mention, but my own searches for anything about Christopher Gilbert Murphy have been just as unsuccessful as yours.
I’m not surprised you haven’t been able to find him, partly because there’s a grade-A mystery surrounding his birth. I found two separate Manchester birth registration records, one in each of the surnames you gave – Murphy and Hooton. Both occur in the same quarter (ending December 1968), and both records give his full name so it would be a remarkable coincidence if these two records are not linked in some way. I'm assuming you already have a certificate ?
I’ve also had a quick dip into Scottish BMD records and there’s neither marriage nor death reported under either of his surnames. Have you considered a change of name through adoption, or just a change of name for some other reason ? Or perhaps he emigrated ?
If he was still using his given names, these following marriages extracted from the free search at
www.findmypast.com are possibilities. (You can use this facility to check all BMD records but you have to pay for the detail and you'd still have to buy the certificate because you won't get much more than the spouse's name from payment to the 'Find My Past' website)
MURPHY Christopher G England Hampshire, Winchester 1982
MURPHY Christopher G England Kent, Ashford 1983
MURPHY Christopher G England Lancashire, Blackpool & Fylde 1985
MURPHY Christopher G England London, Greenwich 1985
MURPHY Christopher G Wales Glamorganshire, South Glamorgan 1995
MURPHY Christopher G England Wiltshire, Swindon 1999
MURPHY Christopher G England Yorkshire, Bradford 1999
MURPHY Christopher G England Lancashire, St. Helens 2000
MURPHY Christopher G England Durham, Stockton 2001
MURPHY Christopher G Wales Glamorganshire, Glamorgan 2002
There are no marriages registered for 'Christopher G Hooton', but I did find these two, both of which might be too early for someone born in 1968
HOOTON Christopher England Northamptonshire, Peterborough 1981
HOOTON Christopher England Sussex, Chichester 1985