Lane reduction arrows

Where you'll see it

On a multi-lane carriageway

What it means

To warn that the traffic lanes are reduced from the left (WM6.1) or right (WM6.3) or from both (WM6.2) sides

What you must do

Change lanes in time if the lane you are travelling in ends. Check both the blind spots where two lanes end from both sides to make sure there is no other vehicle that is also changing lanes

Source: Signs manual