not sure how specific counties run their music BTEc but if you have a Cadet Force Band detachment they're the best people to speak to.
Otherwise HQ Cadet Force Music or the CVQO would be able to help with details about the BTEc. The qualification isn't too hard - especially if your cadets are doing GCSE/A level music as some of the BTEc modules can be completed with coursework etc
You can contact the Royal Military School of music at Kneller Hall. The recruitment department has number (which they gave to me and lost, sorry) of a guy who is the director of music for ACF music. He will be able to tell you all about this kind of stuff and I believe there are courses and dates in Liverpool in October.