If I remember aright, which may be open to question to start with.... the bugle was primarily an instrument for mounted regiments. Infantry would parade with bands, but in battle, bandsmen acted as medical orderlies, stretcher parties etc. Infantry drilled and moved in column and/or line on the battlefield to orders relayed as signals by the tap of drum and/or possibly a fife. The highland regiments were different - of course some would say the pipes are a weapon of war in their own right and should be banned under the Geneva Convention.... Anyway, some officers or sergeants would also carry a whistle.

Cavalry units obviously could not carry a drum (or bagpipes) for this sort of thing, and so a trooper with a bugle remained by the commander's side ready to sound the ordered command. Initially, this may have been a very simple sequence of notes ascending/descending. Simple things do tend to get fancier with use, as many folkies may have found, so buglers would tend to add flourishes etc..

When the rifle appeared on the scene around 1800, the 95th were trained to act independently, and so were equipped with horns or bugles instead of the drum to relay signals, and this appears on their badges. This could be the origin of the use of the bugle rather than more conventional band instruments to sound certain calls in British infantry units. Seems logical, comments ?