This company founded in 1989 and named for its founders Ivor and Shaun Pneumatics. The rifles are made by Shaun Hill (Ivor's son) in Walsall, a town in England's Midlands.
The Spartan is a handmade PCP based on a full-bore hunting rifle, with an air cylinder concealed in the stock.
An ISP publicity video is here:
These rifles sold at auction:
JS FINE ART AUCTIONEERS & VALUERS
Banbury , Oxfordshire
24 Jan 2019
1.A RARE HAND MADE ISP SPARTAN AIR RIFLE 0.177 SERIAL No.587.- FIGURED ENGLISH WALNUT STOCKED- ENGRAVED ACTION BY DON BLOCKSIDGE
2.A RARE HAND MADE ISP SPARTAN AIR RIFLE No.10 WITH LEATHER STRAP. AMERICAN WALNUT STOCK ENGRAVED
Pics from the official ISP Facebook website: