Changing traffic lanes
Don’t move from one traffic lane to another without good reason.
You must give way to traffic already in the lane into which you are moving.
How to change lanes safely
If you have good reason to change lanes, use your mirrors and check in plenty of time to ensure that the way is clear. To check your blind spot when travelling at speed, take a quick sideways glance to check the position of a vehicle that may have disappeared from your view in the mirror.
Signal your intention and change lane when it is clear and safe to do so.
When in a lane or approaching a junction, obey any road signs or
markings (usually arrows) indicating the direction that traffic in those lanes must take.