If the vehicle in front has its right indicator on, but the driver signals with their arm that they are going to turn left, which signal should you take into account?

Correct answer

The one made with the arm.

As a general rule, light signals are used to warn other road users, although acoustic signals and arm signals may exceptionally be used to indicate the manoeuvre, provided they are noticeable to other users. The latter take precedence over light signals and cancel out any other contrary optical signal.