Traveller Heritage?

[heywood]

That family are shown in 1939 register in Mitcham.

[Talacharn]

What was your father's first name? There are several registered in 1955 Oxfordshire.

[heywood]

Another question - sorry. You say:
“ Finding black and white info on him has proved to be almost impossible. He didn’t even seem to appear on my mothers birth registration. ”

Do you have your mother’s birth registration?

Do you remember her mother’s first name being mentioned?

[Milliepede]

Cornelius F Chapman to Calina/Catina Powell

Helpfully that marriage is online.  Feb 19th 1911 Mitcham.

Cornelius Fenner Chapman 23 labourer father James Chapman stoker

Calina Powell 20 father Henry Powell hawker

[heywood]

Looking at 1939, we can’t mention details there is a female near the Chapman family whose names has been amended through marriage.
There is. Marriage - Free BMD
1940 Surrey Mid E
Lily H Gorey and ? Chapman (no Chapman shown).

Also show though
Cornelius F Chapman and spouse Corey but no corresponding name.

I can only see one birth which is  1944 and is one of the family names.

I hope this makes sense.

Perhaps Cornelius and Lily separated.
** added - according to electoral registers Cornelius and Lily are living together.

[Ruskie]

Cornelius F Chapman to Calina/Catina Powell

Helpfully that marriage is online.  Feb 19th 1911 Mitcham.

Cornelius Fenner Chapman 23 labourer father James Chapman stoker

Calina Powell 20 father Henry Powell hawker

This Chapman family with father James, and wife Keziah and children including a 17 year old Cornelius are on the 1901 census. Age doesn’t quite tally.

[heywood]

Cornelius F Chapman b 1920, died 1994 Wandsworth.
Wandsworth covers Stretham so fits with OP’s recollections of grandfather.

[Milliepede]

If you look on Free BMD index there is a marriage with all 3 names you mention.

Chapman
Pratley
Marshall

Fairly recent though so may still be living (1973)

Wallingford district

[heywood]

Lily Hannah Chapman birthdate 31st August 1919 (fits with 1939)
Death 1977, Merton.