I have now ordered the Will for Mary Wallace.
Many thanks to you Rosie99 and everyone for pointing me in the right direction.
The England Registers show Constant Joseph jnr and Edward living in the Deptford area but not for the same years. I've not come across a death notice for Edward yet but will keep searching.
I have now also found via Ancestry and typing in Edward Wallace, my Godfather travelling to Africa in 1952 as he was involved in a Locust survey and this fits in with what I remember my father used to talk about. The jig-saw is coming along!