Old thread, and the OP is no longer around, but I now know what this is and provide this update for posterity.
It’s a British T Friction Tube, Mark IV. This was a single-use brass igniter designed for breech-loading artillery guns with bagged charges, functioning via a pulled lanyard. The tubular part containing an explosive compound fitted into the breech vent, and a yank on the lanyard attached to a metal loop pulled a friction wire through it for ignition to detonate the main charge.. The loop is missing on the found item because it has been fired.
The Mark I friction tube was designed around 1897 for artillery pieces such as 5 inch and 5.4 inch howitzers among others, and Britain entered WWI with a number of old 15-pounders that still used these igniters, updated to the Mark IV in 1914, and largely phased out by 1916.
View attachment 2261323