QVC The 26th (Cameronians) Regt of Foot officers large 25mm button in absolutely mint condition.

The 26th (Cameronian) Regiment of Foot was a Scottish infantry regiment of the British Army, active from 1689 to 1881. Under the Childers Reforms it amalgamated with the 90th Regiment of Foot (Perthshire Volunteers) to form the Cameronians (Scottish Rifles) in 1881. So any button bearing the “26” regimental numeral dates to before that amalgamation — this is pre-1881.
Dating the Button
The back reads “Firmin & Sons, London” — no “Ltd” suffix and no street address. Buttons bearing the backmark “Firmin & Sons” date to the early 1850s through to 1875, after which the firm became “Firmin & Sons Ltd” and the backmark changed accordingly. So this button dates to roughly 1852–1875, firmly mid-Victorian.