Hi Chris, thanks for the information.
It looks like the Seaton's you found in 1901 are the correct ones since Annie is the correct first name although I still need to confirm if her maiden name was Haddow. Jessie could indeed be my grandmother since the age is correct although I'm not certain where her first name of Gladys came from but it must be back in the family somewhere. I think the fact that Haddows lived next door adds further proof that these are indeed my ancestors.
I'm still a little puzzled why she would have used Haddow on my dad's birthday certificate and Seaton on his marriage certificate.
Could I ask a favour if you still have access to the 1891 and 1901 census to look up my ggf Edward Hunter (born in Sanquhar?) whose wife's names is Jemima (Robertson) to see if they were in New Cumnock at these times.
Thanks again for all your help.