Are PhD students allowed to teach final year university cles by themselves?

I'm in my final year at university in England and for one of my cles the professor has three PhD students that accompany her every week. She has frequently left one or all of them to teach the two hour cl when she has not wanted to or been unable to come to the lecture. Are PhD students allowed to be teaching so many of these cles unsupervised when they are essentially not qualified to be university lecturers yet? I want to lodge a complaint against this professor for her unprofessional behaviour, but I would like to have everything clear before I do so.