Wikipedia
Brigadier-general was formerly a rank or appointment in the British Army and Royal Marines, and briefly in the Royal Air Force. It first appeared in the army in the reign of James II, but did not exist in the Royal Marines until 1913. In the 1740s, the substantive rank of brigadier-general was suppressed, and thereafter brigadier-general was a temporary appointment only, bestowed on a colonel or lieutenant-colonel (or on a colonel commandant in the Royal Marines) for the duration of a specific command.
The appointment was abolished in both the Army and the Marines in 1921, being replaced in the Army by the appointments of colonel-commandant (which already existed as a rank in the Marines) and colonel on the staff. Colonel-commandant was in turn replaced by the appointment of brigadier in both the Army and the Marines (although not replacing the substantive rank of colonel commandant in the latter) in 1928. From the formation of the Royal Air Force on 1 April 1918 until 31 July 1919, it used the appointment of brigadier-general. This was superseded by the rank of air commodore on the following day.
The rank insignia for appointment of the brigadier-general was a crossed sword and baton; the insignia for higher grades of general consist of this device, with the addition of a star (major general), crown (lieutenant general), or both ("full" general). The equivalent naval appointment was commodore.
Brigadier is the highest field officer rank (hence the absence of the word "general"), whereas brigadier-general was the lowest general officer "rank". However, the two ranks are considered equal.