The police have no right to shoot anybody and never have had. They have no right to shoot at anybody. This is not a banana republic. The police are subject to law, and in Britain, the police have the status of unarmed civilians with special powers. What armed officers have is a dispensation to discharge firearms in situations where a lawful justification or legal defence applies. The burden is on the police to demonstrate that such an exceptional course of action is justified according to law. Even in 1985, there would have been an inquiry, the officers involved would have been suspended (on pay) and questioned under caution, and their firearms would have been submitted for forensic examination. That was standard, even then.
Authorised firearms officers know this will happen and the raid group officers who entered the farmhouse will have known this. The overarching point is that these officers know if things go wrong, their actions, even if justified, will come scrutiny - and rightly so. I think it follows that there is a reasonable possibility that firearms officers will collude to present facts in a certain way, so as to defend themselves. This is just human nature.