Unmarked repeating air rifle (1980s/1990s?, ASI prototype?)

Unmarked repeating air rifle (1980s/1990s?, ASI prototype?) 

Pics copyright Holts Auctioneers.

Keith said this on the airgunbbs.com in March 2024 in answer to a query about its origins:

Yes, I first saw that in Terry Robb's shop about ten years ago, he showed it to me. It was beautifully made obviously by a very skilled man. No identifying name or anything on it as to who made it. Terry suspected it was a homemade special & i agree. I tried to buy it at the time & offered £400 but he wouldnt sell.
It was sold a few years later to one of our members the late Pete Basham, Pete pestered Terry for months & eventually managed to buy it.
Pete passed away last year & his collection went to Holts for disposal. Quite a few of his air rifles & pistols were in the last auction & this one.