Well I found your parents' marriage, after that it gets difficult...
"England and Wales Marriage Registration Index, 1837-2005," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:QV63-NQ8G : 8 October 2014), Lynne Sandford and null, 1965; from “England & Wales Marriages, 1837-2005,” database, findmypast (http://www.findmypast.com : 2012); citing 1965, quarter 4, vol. 1A, p. 482, Darlington, Durham, England, General Register Office, Southport, England
Given the very young age of your mother I doubt Davy was much older and IF he was born in County Durham then there's only one good fit:
"England and Wales Birth Registration Index, 1837-2008," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:QV7H-J7ZX : 1 October 2014), David Richards, 1947; from "England & Wales Births, 1837-2006," database, findmypast (http://www.findmypast.com : 2012); citing Birth Registration, Gateshead, Durham, England, citing General Register Office, Southport, England
However, he could easily have born in a neighbouring county, or indeed anywhere so this is very tentative. You could try ordering a copy of the marriage certificate from the general records office (it's £9.25 I think) if you don't have one. It might have some additional info.