Is there a Logical Answer?

[Sloe Gin]

My  birth certificate (England pre 1969) has my forenames plus my father's surname in the space for child's name, this would tell me very clearly what my registered surname is.

As per the reply above, my English birth certificate, also pre 1969, clearly shows my name with a first name and a surname.

Mine does not give a surname.  Only my forename. 
The column is headed "Name, if any" and there is no mention of surname in the column heading.  There is mention of surname in the column headings for parents' names, so they were required.

It looks as though the registrars took it upon themselves to add surnames in your cases, but no surname was asked for in the format.

I have lots of old birth certificates (as I'm sure you all do), and none of them show a surname for the child - only forenames.

@AntonyMMM, can you comment on this, please?

[Sloe Gin]

Here's an example from the same period as mentioned in the OP.

[majm]

Surely on the E & W birth certificates, pre 1969 if there are names in the space under the column heading "Name,  if any"  they are legally the given names, even if they may well be surnames within the family.

May I also suggest that the baby does not actually have a surname, and even if the name of the father is provided and even if the father is the informant, that is not where we should anticipate finding baby's surname.   

Surely pre 1969, E & W births have the baby's surname coming directly from the column "Name and Maiden Surname of the Mother".   So in the example that Sloe Gin has provided,  baby George gains his surname from the name his mother was recorded as .... Mary Ann READ.   Yes,  George's dad was James READ but that's not why George would likely be George READ.   

I can assure you that in New South Wales, Australia until 1969, baby's birth registrations had no provision for a separate column giving a surname for baby.   I can further assure you that among my retired ancient living rellies are former senior officers of NSW BDM.  They assure me that no one ever believes them BUT they know a child's surname comes from the surname that MUM was known by.  If a married women in that era, she was likely known by the surname of her husband.  NSW inherited that habit from .... England & Wales, and not from Scotland.

JM

[Rosinish]

Headings of columns on Scottish BMDs...

One of the upsides of Scottish records, probably the best in the world.

Annie

[LizzieL]

My  birth certificate (England pre 1969) has my forenames plus my father's surname in the space for child's name, this would tell me very clearly what my registered surname is.

As per the reply above, my English birth certificate, also pre 1969, clearly shows my name with a first name and a surname.

Mine does not give a surname.  Only my forename. 
The column is headed "Name, if any" and there is no mention of surname in the column heading.  There is mention of surname in the column headings for parents' names, so they were required.

It looks as though the registrars took it upon themselves to add surnames in your cases, but no surname was asked for in the format.

I have lots of old birth certificates (as I'm sure you all do), and none of them show a surname for the child - only forenames.

@AntonyMMM, can you comment on this, please?

My birth certificate has no columns for parents names

[majm]

Perhaps you are looking at a "short form"  rather than the "long form" document.

JM.

[Pheno]

Yes mine is a short form certificate - but the only official document presented to my parents at time of my birth (in fact I wonder why after all these years of genealogy I have never got a long form of my birth certicate).

It quite clearly says name: and alongside it my full name: Josephine Edge (not my real name) so I have both a first and last name.

If that is all most of our ancestors had in their possession then they do show a first and last name.  If not presented with a full certificate why would they ever purchase one - I have got through modern life without requiring one

Pheno

[LizzieL]

Yes mine is a short form certificate - but the only official document presented to my parents at time of my birth (in fact I wonder why after all these years of genealogy I have never got a long form of my birth certicate).

It quite clearly says name: and alongside it my full name: Josephine Edge (not my real name) so I have both a first and last name.

If that is all most of our ancestors had in their possession than they do show a first and last name.  If not presented with a full certificate why would they ever purchase one - I have got through modern life without requiring one

Pheno

Me too

[Pheno]

Just to add - when you are all ordering birth certificates from the gro you automatically get a full (long) birth certificate and assume that the person concerned also had that, thus showing all information, some of it contrary to what was used in life.

As proved by Lizzie and I not everybody was provided with a full birth certificate and may not ever have purchased one so there is a name on the full certificate which is likely to have been used as their official name in life and maybe a different one to that they were known as.

Does anybody know when short certificates were replaced by long ones?  Mine was issued in 1956 but both my sister 1959 and brother 1961 have long certificates, but they were both born in a different county to me.  Could that have anything to do with it?

Pheno