It may seem odd to reply to my own post!  

  However, I am pleased to have found a possible baptism for James Cook in a transcription on another website:  baptism St Peter's Overseal, 20th March 1791, son of John and Ann.  
However, I still don't have a marriage between James Cook and Sarah, probably about 1815 in Overseal or Netherseal.  Can anybody help with these parish records, please?
... and since the above is a transcription, does anyone have easy access to the microfilms to confirm, please? 
Mike