This is a bi metal cap badge worn by an enlisted man in the Prince of Waleses’ Leinster Regiment.
The Leinster Regiment was one of the Irish Regiments disbanded in 1922.
This cap badge has a number of interesting features. With the large sweat holes to the rear and considering their shape, we can conclude that not only is this an excellent feature only found on original pieces, but also the shape suggests an early date of manufacture. I’d suggest that this badge is late 19th century or early 20th century. There is little doubt that it predates the Great War by a fair number of years.