art2and art.3 could impose postive obligations on the authorties o takemeasures to protect individuals at risk of serious harm from thecriminal acts of others. When considering whether those obligationshad been complied with, account had to be taken of the difficultiesคoง.t)วลขากinvolved in policing modern societies, the unpredictability of humanconduct, and the resource and priority-driven operational choicesthat had to be made. The police had to be afforded a degree ofdiscretion in taking operational decisions. Police forces facedchallenges that had perhaps been unforeseen when the Conventionwas drafted, and they had developed techniques, such as "kettling",to deal with them. Article 5 could not be interpreted in such a way asto make it impracticable for the police to fufil their duties, providedthat they complied with its underlying principle, which was to protectthe individual from arbitrariness. Nor was it concerned with mererestrictions on liberty of movement. The difference between adeprivation of liberty and a restriction upon it was one of degree, andtherefore the type, duration, effects and manner of implementationof the measure used had to be considered.