Here is some of what you need to know about checking the mirrors.
You must check behind before
- Changing speed
- Changing direction
If you intend to slow down you must check behind before doing so. This will give you an idea of whether what you are about to do will affect a driver behind. You may find you need to brake early and more gently if someone is very close - in order to minimise the risk of a collision.
If you intend to accelerate you should check to make sure no vehicles are overtaking. If they are you may need to delay your acceleration until they have passed.
If you intend to change your position in the road you must check the appropriate mirror to see if what you are about to do will bring you into conflict with another road user. This includes each time you pass a parked vehicle or cyclist. Check regularly so that no vehicles can move into your blind spot without your knowledge. Remember Mirror - signal - manoeuvre.
Check behind before signalling to ensure that your signals are well timed (to avoid confusion or alarm) and also to ensure that what you are about to do is safe. Brake lights are a signal, so check before braking.
The only time you should not check behind is when you must stop in an emergency and where it is imperative that you stop quickly. However, a good driver will always have an idea of what is going on behind them.