Roy, may I suggest that you buy the death certificate (from GRO) for Harry who died Sheffield in 1984. That will tell you who reported the death (maybe a wife or child) and an address.
Dave
Roy,
There is a tree on Ancestry which has your Harry Smith. It says he married Theresa Coleman. The marriage in1948 is on Free BMD ,as are the births of their 4 children.
Dave
You probably need to search the Electoral Registers.
A quick search brings up Stuart S Wilkinson, Max Wilkinson and Jane C Mansfield living in Newcastle Emlyn in Wales in 2002-2003, 2005,2012 and 2013 - cant see anything obvious for them after that.
So you might need to use something like https://www.192.com/. An initial free search will bring up basic information (as above) but there will be a cost for getting any full address if you find them.