OK, I got it wrong! A rather helpful chap from DSGi Head Office got in touch and pointed out that Jessops have never been a DSGi operation, stating:
“…in the UK DSGi operate Dixons, Currys, PCWorld; TheLink has sort of finished and is web only, as is Dixons, except the Airport stores. (There are also lots of European chains, which have names I can never remember); but Jessops has never been a DSGi operation.”
A couple of other comments from several folks indicate that Jessops competence is still very much changeable and your mileage will indeed vary. I must have been lucky!
Anyway, I won’t name names on this but thankyou for the clarification and consider me corrected.