What information that we have makes this a "worrying development"?

The law on force (for police or anyone else for that matter) is pretty clear cut and the law (and guidelines in interpreting that law) hasn't changed for years.

The bottom line is that if there is a serious and immediate threat to life then a very high level of force indeed may be justified.

It's funny how people express a great deal of concern for the chap who was shot but not for the police officers that he apparently tried to kill.