Some sort of professional negligence. Many other people should have been charged as well.
It may well be true that there is no specific law he has broken, that's part of what I'm raging against.
I accept that the post-80s regime of light-touch regulation means that these people were basically doing what they were supposed to be doing, and that kinda makes it impossible to punish them.
While I am no fan of ex-Sir Fred I'm struggling to think of what criminal offence he should be charged with.