I think the problem is rigidity in the methods of the police/army.

Based on the training and technology they have, how fast can they adopt and deploy new technology like the "drones" without going through the procurement nightmares ?

Second thing to consider, training personnel to control the robots and the drones. They will not allow those guys in KTN feature etc to fly and control these things for security reasons.

Would they be willing to train or acquire IT staff (or defense arm) just for these sort of intelligence gathering ?

Third, old school thinking may shoot down this idea because they may think that the drones may scare the masked-men into undue aggression.