A TLR for taking on the teaching of an A level? I can't see how that could possibly be justified. Sole teachers of minority subjects exist in many schools - often, a newly qualified teacher will take on A level, GCSE, etc in their minority subject as the sole teacher. It's good for your cv - but not a cause for the award of a TLR, in my opinion. (Middlemarch, appointed sole teacher of a subject in 1981, teaching it to A level, O level, CSE).