OK I'm a bit confused about whether to use indicator or not when passing a stationary car/bus etc.

My driving instructor told me that it's not necessary to use indicator when passing a stationary car/bus specially when there's a left/right turn road and she also told me that the examiner will failed me if I indicate when passing a stationary bus while there's a left/right turn road.

I've spoken to a friend of mine who just passed his practical driving test and he said that I must use indicator when passing a stationary bus.

So I'm now confused!