Its a cocking piece from a (Charger Loading) Long Lee.
One of the variants has no safety either on the receiver or on the bolt, and has a plain cocking piece like this.
I have/had one of the rifles. I used it in the UKmilitary Methuen competition one year - I recall there was a stage where the line of troops/firers (civilian service rifle clubs taking part alongside military teams) had to advance to the next 100yd point with rifle loaded and safety applied. In my case the RCO agreed that I'd advance with the bolt open, as the rifle had no safety mechanism at all!