Oratory DS1 moved schools for sixth form, partially to make sure he could do CS. His old school lost their CS teacher in May of Y11 and dropped the A level, so DS1 started doing CS at his new sixth form. They had also lost their CS teacher in May, but had managed to appoint someone. This last minute appointee turned out to be useless (DS and his mates actually complained) and left in October of DS's Y12. They couldn't find a replacement until April of Y12, so DS and his classmates taught themselves. He took the AS level at the end of Y12, got an A (!) but decided to drop it and concentrate on his other 3 A levels.
Recruiting and retaining CS teachers is a very difficult job. Most computing types can earn more money actually programming rather than teaching. And teaching is definitely not an easy option.
DS1 is just finishing his 2nd year at uni, doing maths and wants to be a programmer eventually. You don't need a CS qualification to get a job in the industry. You don't need CS A level to do a degree in CS.
However, DS3 will be doing CS A level, at yet another different sixth form. I hope he has more luck.