One of the two return springs, per wheel, for Mini single-leading front drum brakes 1959-64 and all Mini rear uppers.
This is the one with the coil in the centre of the spring.
A good mechanic will replace the pull-off springs
17H8092) and
17H7621 when installing new shoes. The return springs rust and fatigue over time and may have been damaged by improper installation in the past.