No Deed-poll record found

[paddyhaig]

My mother passed away a few years back, and it was found that the name on her birth certificate is different than the name used on my birth certificate. Apparently, I was informed, that her step mother had insisted that my mothers forenames be changed at some point in her childhood. I have searched high and low for official deed-poll records in many places, including the gazette and national archives and have found nothing, that would give any official recorded sanctioning to the matter. I now need to legally tie these names together so as to prove my lineage on my mothers side.
I have a number of other documents, such as my mothers death certificate and my parents marriage certificate. I can loosely tie these documents together, in that the place and date of birth on my mothers birth certificate and her death certificate are the same. Also, her parents names, occupations, and mothers maiden name, are the same on her birth certificate bearing her earlier forename's and her marriage certificate bearing her later name. To me it seems pretty obvious what I am tying together here is legitimate, however others might not see it to be so. Can anyone suggest anything? Like a legal document that I might try to acquire that could bring some legally acceptable validity to my claims? A 'Declaration of parentage' has been suggested, but the 'Declaration of parentage' form, seems to be very complex and I'm not even sure that I'm following the correct path. Pleas someone help me!