Winnie, I have been trying to find your grandfather, but there's not much to go on. I did find a John Johnson born in Orrell in 1925 but that's not really much help to you, as it's not necessarily right and in any case it doesn't get you any further.
Do you know your grandmothers Christian name?
Your grandfather must have died young if your grandmother was a widow in 1960s, could he have died in the war?
On this database his birth is registered as in Wigan, but on Lancashire BDM it's registered as Orrell.
England and Wales Birth Registration Index
Name John Johnson
Event Type Birth Registration
Registration Quarter Jul-Aug-Sep
Registration Year 1925
Registration District Wigan
Event Place Wigan, Lancashire, England
Mother's Maiden Name (not available before 1911 Q3) Atherton
Line Number 7