I managed to track down the location of the burial registers for Doddington Road and London Road cemeteries in 2018. I was told they are held by a company contracted by the council to maintain the cemeteries, called Wellingborough Norse. I contacted the company, they took the registers from the safe to do a quick cursory search for me but had no luck because apparently the registers are in no chronological or logical order. Very frustrating knowing two of my ancestors must be in there! I’m surprised they’re not being transcribed, or transferred to the record office or something. Though I don't know if the situation has changed since I contacted them...