I managed to locate the birth record and got a digital copy.
Ernest Stanley Rooke born 13th December 1920
Mother listed as Ruth Rooke (Domestic) from Hemswell Lincolnshire.
Looking in 1921 Census I have located Ruth Rooke as a Servant without her child she is only 18 so was 17 when she had Ernest.
I have learnt from Ernest's Son that his father moved to Northern Ireland with a friend after the 2nd World War as he believed he was an Orphan and had no one to go home to. I suspect. as his mother was young, unmarried and in service she gave Ernest up and he ended up in care. Ernest believed he was from Barnsley in Yorkshire so it is possible he ended up in a carehome/orphanage there.
1921 Census - Ruth Rooke (Ernest's mother):
https://www.ancestry.co.uk/imageviewer/collections/63150/images/15590_02031921 Census - Ruth Rook (Ernest's Grandmother):
https://www.ancestry.co.uk/imageviewer/collections/63150/images/15590_00311911 Census - Ruth Rooke (Ernest's Mother and Grandmother)
https://www.ancestry.co.uk/imageviewer/collections/2352/images/rg14_20124_0031_031901 Census - Ruth Rook (Ernest's Grandmother)
https://www.ancestry.co.uk/imageviewer/collections/7814/images/LINRG13_3108_3112-0417