Self defence?

Ok, so I'm bored. I've just been re-reading the response from Downing Street regards the petition to allow security personnel the use of batons/sprays and handcuffs as standard, to which they basically gave a big no.
I came across a section on the use of reasonable force:

Under the law as it stands a person is entitled to use reasonable force in self-defence, to protect another person or property, to prevent crime or to assist in the lawful arrest of a criminal.
What constitutes `reasonable force' will depend upon the circumstances of each case and is a matter for the courts to decide. The courts have held that if a person does only what he honestly and instinctively thought necessary to defend himself or prevent a crime, then that would be potent evidence that only reasonable defensive action had been taken.

Now, the way I read that, if your first instinct when someone pulls a knife/whatever on you whilst not on duty is to punch them full-force in the face, breaking their nose/jaw/whatever else you come into contact with, that would be reasonable force. So in theory, this would be the same if we were on duty at the time this happened, wouldn't it?

As a private citizen, we could defend ourselves in that way and it would be called self defence, however, whilst on duty whether it be in a pub or club, or a retail site, or even in some remote building site, we are seen as having a position of authority, and if we did this to defend ourselves on duty, we would be considered as thugs who beat up people rather than attempt to disarm them without having to resort to violence.

It's a very grey area, but until it is clarified we are going to be constantly on a knife-edge (no pun intended) if someone tries to attack us in any way shape or form, wondering if we would be sued etc if we seemingly go too far.

Gordon, get your ass into gear and allow us all to defend ourselves properly. The criminals use weapons on us, so why can't we use 'defensive' weapons on them?