mvpel,
Given how I've lived in this house for about 5 years without ever properly meeting my next-door neighbour on the left side (my right-hand neighbours are quite nice, though), I'd say it's a reasonable probability that the DG didn't know his building was under surveillance for terrorist activity.
Also, given my experiences with the UK constabulary, I'd say it's more likely that the plainclothesmen just shouted "Oi! You!" or something similar, rather than "Halt! Armed police!". See previous page. The most likely explanation for his behavior is just seeing normally-clad men waving guns and shouting.
I don't think anybody will be running from normally-clothed people with guns in the future. I'm sure this will make for some very successful muggings in the Manchester, London and Liverpool areas, too. How smashing.
How absolutely smashing.
To be honest, putting this on the Dead Guy is really rank. He didn't commit suicide by cop, because this is the first time in decades that anything like this has happenned.
To be honest, if they were that worried about casualties, it would have made a lot more sense to have taken him down on the empty bus he was riding, down a street with few pedestrians.
This is rank incompetence at best, and while I'm not known for my tinfoil beanie habits, the conspiracy fans who're bleating that SO19 wanted to send a message may, after all, have a point. They had plenty of opportunity beforehand, and I'm constitutionally disinclined to place great faith in any "organisation" of people.