It is by far the oldest and most extensive standards body in the world, originating from a meeting of various institutes in 1901. This created a long running committee structure that exists to this day.
The standards body evolved into the "British Engineering Standards Association" in 1929. In 1930, it finally became known as the British Standards Institution.
BSI currently operates in over 100 countries and publishes over twenty thousand standards. Not surprisingly, the prefix for BSI standards is 'BS' (as in BS7799-2).