They have tried this before, many times, both in London and in other big cities. A group of youths, standing chatting, on a street corner, is not always a gang. But these are the youths who are constantly harassed by the Police because they are deemed to be safe targets by the Police. They get their 'stop and search' numbers in the book without too much effort on their part.
What is needed is for the Police to move in to a flat, in the area, as a couple. They can then go about their normal business of living in the area and listening to what is happening. That, to be, would gain much more intel and be far cheaper than running round in vans, ready to pounce on kids, who, in general, are faster runners than the Police.!!