Update:
Having at last managed to get a certified copy of the marriage certificate of my 2* great grandfather, Charles Atha (b. c1819 in Leeds) and his wife, Mary Fearnsides (b. c1820 in Leeds) I have found that his father was called Martin and not George as previously seemed likely.
Mary Fearnsides father was called Benjamin. I haven't found any further information on these people yet.

Both Mary and Charles surnames were mispelled on the Birth index - hence my problem finding their marriage certificate (Fearnsides is the maternal surname on their son, Samuel's, original birth certificate which I obtained through the family.)