There was a lot in the Swan collection number 942, described as a BSA underlever development rifle based on the Airsporter Mk II. with rising Breech .22 cal. serial number RW 1056 (Roger Wackraw).
I've never seen another, did anything come of the development? The system looked similar to the one used on the Merlins.
I had a bid on it but let it go and am now feeling some regret.
Mel.