Could the Parsons Green bomber have been stopped by citizen action? Quite possibly.
We could widen our attention as little children do and probably spies do, too.
We all like to lose ourselves in our mobile phones or books on the usually uncomfortable tube ride to work. So if someone gets on the tube with a bomb and then leaves it there we are unlikely to notice it. What if we all took notice of our surroundings? Not necessarily all the time but just at stations, and note who gets on, what baggage they are carrying, and who gets off and whether they have forgotten their bag.
If only ten percent of us did this then the risk of a repeat incident on the tube would be much less.
I have the number of British Transport Police listed on my phone under BTP. Thus it would take at most six keystrokes to call them (phone - contacts - BTP - call). The number is 61016. If you commute in London, put it on your phone now, and stay alert at stations.
This also gives us opportunities to come into the present moment and out of the mist of imagination in which we dream into work.