In short
MSM stands for Mirror–Signal–Manoeuvre and is the order to use for every change of speed, direction or position: check the interior mirror, then the relevant door mirror, signal if needed, then move. A missed mirror before changing direction is the single most-marked test fault.
Updated 2026-06-06 · 5 min read · By Driving Routes Editorial
The order matters
It is always M-S-M, never S-M-M. A signal before a mirror check tells other drivers your intent before you have confirmed it is safe.
When to apply it
Every change of direction, every change of lane, every meaningful change of speed (slowing for a junction, accelerating to merge), every move off from a kerb.
The longer version: MSPSL
At junctions, the full sequence is M-S-P-S-L — Mirror, Signal, Position, Speed, Look. Position the car correctly for the turn, slow to the right speed, then look both ways before committing.