This would be laughable if it weren't so serious. The criminal element is deterred only by fear of arrest or death, and they have nothing to fear.
That used to be the case, but I don't think it's the norm currently. For one thing the BIG BROTHER cameras are everywhere so usually they know in advance there is gunsmoke in the air. I have to hand it to the Brits, when they need to bring force they bring MASSIVE amounts. H&K MP5s usually substitute for handguns in those situations. Also, I don't think their military is limited from running ops on their own soil as we are restricted by the doctrine of posse commitatus. Fact is that terrorism is so much a part of the landscape, they bring in the army at will.