operation london bridge as it's called. i started over 20 years ago. a box got dusted off every year to make sure still valid. there are a number of phases to this operation. the most important one and the riskiest part passed which is managing this enormous queue snaking through london towards westminster. the necht phase is taking place very much inside a secure footprint and it's a footprint that is used many times a year but hundreds times over history to actually conduct such events. i think we're in a really safe part of this operation. >> this is the largest deployment of police officers that the city has ever seen. that is one part of the security operation. with all of the world leaders that we're seeing beginning arrive the at westminster abbey, how do you balance each