The CO2 pistols indeed cannot fire real bullets, BUT they are modified to be just as deadly, Larger callibre and increased power.
And for the statement, i thought there we no guns in london, you must be joking. Alot of the guns that are used however are blank firing guns, that indeed can be and are converted.
But of course the guy was just a nut job racist, anyone can see that, I really doubt obama had anything to do with it.