As said, an early Fenman in a CS800 stock. Cocking buttons are still available from John Knibbs I believe. In excellent working condition with good bluing around £400-£450. Cocking button is not difficult to change, but I suspect a potential buyer would want to make sure everything is good before parting with the top estimate. Close up pics would give us a better idea of true value. Silencer looks very poor in the pic, and I can't quite make out what's going on with the trigger.
John
Law of any kind only affects those willing to abide by it.