For the training you will need to do you degree subject - however afterwards when you get a job you can offer to help out in other depts. and worm your way into a job like that. I am an MFL teacher, but now teacher Physics and Maths (I don't even have a GCSE in Physics, but schools are desperate).
Both DH and I are teachers. DH's degree is not related to the subject he now teaches. Instead he worked for a number of years in his new field and gained a place on a pgce course because of his experience. Some universities are more flexible than others. Our local uni (not the one we trained at) has so few people on their teacher training degrees (60% drop) this year they've been rather open about who they accept.