I am a science teacher and am in demand for boths maths and science at GCSE, I have also tutored for French as a girl I had for maths needed some practice for her Oral Exam and I have French to A-level. I am quite open with people that I am not maths (or french!) trained. Do you have a degree in maths or english? Or A-levels? I am able to do what I do because of my A-levels and my main subject being very numerical. I think if I suddenly decided I could teach English GCSE I would struggle to convince parents!