Yes, you are required to turn on the indicators before changing lanes on a motorway.

The indicators should be turned on well in advance (but not so early that your intentions may be misinterpreted) before you:

• Intend to turn at a junction.
• Intend to change lanes.
• Intend to move off from the side of the road.
• Intend to make a U-turn.
• Intend to turn into a parking space.
• Intend to move your car sideways in any other situation.

Do not forget to turn off the car's indicators after completing the manoeuvre.

Before turning, moving your car sideways or reversing, you must always check your rear-view mirror and side mirrors as well as your vehicle's blind spot by briefly glancing over your shoulder. The blind spot is the area not covered by any mirror.

Read more about the car's light signals