Further to the above I had a lovely chat with John tonight and he remembers the gun well considering this was over 20yrs ago! Much of the information we had was correct as the background to this was that Titan had the main barrell and mechinism made by the chinese military as some of the directors had contacts in this area. The original delivery was meant to be for mostly .22 parts but ended up with nearly all .177 bits. John used these parts and modified elements using components from the BSA Meteor (spring, piston head, washer, etc). The deluxe version we have had the stock made by custom stocks in Sheffield. One of these was either given, or purchased, by airgun world as part of their "spot the difference" competition which is the one won by my father.
As is indicated on the facebook page by the time all the UK work was done the gun became unsuitable for the UK market and never really took off.
He has confirmed that only 4 were ever built in .22 and they were never put into mass production due to the parts issue. There were some built in .177 and marketed / sold as the SL800 but he wasn't sure of the exact numbers.