Thanks to both of you. I'll assume it's a SG40 until evidence to the contrary emerges. Given the postmark, I would assume it's unlikely to be one of the earlier catalogue numbers.
Cover in great condition with embossed envelope, Honeycomb and Garter.
Actually, in person, the envelope is a bit worse for wear having been passed down through the family for 160 odd years.
Lovely Huntley (Scotland) Postmark (New discovery for the database)
Only other strike recorded is 1918
The Keith Backstamp also a new discovery for the Pmk database.
This is very interesting. If I was dealing with a Canadian cover, I would know exactly where to turn for reporting and/or further inquiry. Is there a site you can point me to to report this (assuming you think it's worthy of reporting)? I'm unfamiliar with British postal history groups.