Ca. 1200, plus/minus 100 years.
Grrr, thought I forgot to photograph it but on second thought I am afraid I never actually saw it; it is the property of Durham Cathedral, North East England, not of the Leeds or London museums, and probably not even on display there. I will try to do some research and let you know.
For more information on that and related items, please go
http://bjorn.foxtail.nu/h_conyers_eng.htm
Best,
Michael