Silver & enamel 19th County of London (St Pancras Rifles).sweetheart.

 The maker’s mark is T.L.M, and it stands for Thomas Lyster Mott (subsequently trading as T L Mott Ltd).
Thomas Lyster Mott was a Birmingham silversmith and his mark (T.L.M) is recorded as being seen on items dating from 1918 to 1932, appearing on brushes, compacts, fob medals, frames, jar lids, matchbook holders, and spoons. His father was Thomas London Mott, who used a similar mark and is recorded as early as 1880.
So your sweetheart brooch sits very neatly in that dating window – the Boer War dates on the badge (1900-1902) would fit with a brooch being made in the period when T.L.M was active, likely as a retrospective commemorative piece or produced during WWI when sweetheart brooches were at peak popularity. The T.L.M mark in an oblong surround is seen on other high-quality silver sweetheart brooches, including Rifle Brigade examples, which are noted for their fine workmanship – so he was clearly a specialist in this type of piece.
A quality maker, and a very attractive brooch for the 19th County of London (St Pancras Rifles).​​​​​​​​​​​​​​​​