Thanks so much to everyone who responded to my plea for help regarding pet burials.  It seems this is a topic of interest to many people, but would appear to be very under-researched.  There is definitely scope for a publication in this topic for someone!  If anyone is researching this in future, a respondent mentioned what was turned out to be a very useful paper by Richard Thomas 2009"Perceptions Versus Reality: Changing Attitudes Towards Pets in Medieval and Post-medieval England" In Just Skin and Bones? New Perspectives on Human-Animal Relations in the Historic Past.  BAR International Series 1410, edited by A. Plukowski, 95-105. Oxford: Archaeopress addressed issues such as defining pets.  This paper is available on academia.edu.  Thanks to Craig Cessford for that reference, amongst others.
Regards, Janice