These are sold per bush but fitted in pairs.
Apart from very early cars all minis up to 1996 had 2 of these each end.
From 1996 rover fitted a single silent block type bush which will fit your existing
21A1109 arm (part number usually stamped on arm) later 1275cc cars had a longer bar
21A1817 fitted where the engine was moved forward.
There is also a poly version available as
CRC5329POLY.