Our rank and file coppers are not armed (though I think they should be, at least with plastic bullets, as it would have been a better deterrent to the rioters). However we do have Armed Response teams, so in this case, officers would have reported that the guy had a gun at which point the armed team would be brought in. It may have been the Armed Response officers who were tracking him in the first place.
I believe some other sections of the Force are armed as well. Such as the ones who guard Number 10.
