Hi. Difficult to value without photos, but unless the above rifle sports the factory etched Jubilee '55 moniker denoting 50 years since being officially available in the U.K., it is actually a current model, ergo still available new.
This in mind then, I'd bring the std second hand rule of thumb in of 2/3rds price when new (currently £300 with mod, so looking at £200 inc. mod), minus £25 for the chip in stock, as being laminated, this will be very difficult to have repaired invisibly
So my best calculated guess here would be £175 for the rifle as detailed inc. mod, plus maybe £45 for the scope and mounts, so for the combo, you are probably looking at a s/h value iro £220 (plus post). Hope this helps . Atb: G.