The scope sounds like the one that was intended for the BSA Merlin. I'm surprised you managed to get it to fit on a MkII Airsporter, as I was under the impression that the Airsporter of that time had the same dovetail fittings as the Mk II Meteor. These were extra wide at about 15mm.
The Merlin scope I had certainly wouldn't fit on my Mk II Meteor.