The police guidelines on appropriate use of firearms are NOT a Licence to Kill.
The prosecution have the task of proving that F's bullets actually killed Y; that F himself aimed the gun and pulled the trigger; and that F actually intended to kill Y -- but I assume these things follow straight from the video.
The guidelines do not change the law. They explain what self-defence (or justifiable homicide) actually means, when it comes to protecting the public from a threat, i.e what are the limits of what is allowed by law. They refer to previous police killings, and explain how the courts decided those cases. Again, the guidelines do not change the law.
If F had only fired one shot, he might have got away with claiming that he only meant to wound Y, or even that the gun went off accidentally -- either of which might get the charge reduced to manslaughter. But eight shots rule out any kind of "I swear I didn't mean to kill him, your honour".
F's only hope is to prove he acted in self defence.
The facts that F fired 8 shots, and that he fired the shots in two bursts, are not relevant. They do however rule out any chance that F could argue that he didn't mean to kill Y.
Again, the "attempted" change is in case it turns out that the evidence does not prove that F's bullets were the actual direct cause of Y's death.