I think AJH93 needs to advise obtaining a copy of either the 1943 or 1958 marriage certs to establish the name & surname of Agnes's father. If she was born 1926 she was barely 17 in 1943 so unlikely to have been previously married.
There is no fitting birth for an Agnes Gordon Redmond in England/Wales/Scotland
If Joseph Britton was the alleged father of a child born c 1944 & allegedly married to the mother - the birth cert should give parental details,
Or do you mean he was married to someone else?
His 1955 marriage cert should show his marital status - as mentioned above - he was 40 so may have been previously married