Someone at the US:NI investment conference was getting a police escort from the Hilton to the morning session. So the taxi driver blocking the way was asked to move on. Several times.
Another car decided to stop at the roundabout let someone out. And no one reckoned on the learner driver who pulled out in front of everyone and slowed the whole procession down.
Not to mention the traffic lights crossing Oxford Street that eventually slowed the cortege down to a stop. Not as slick as the 40-50 mph escorts that top politicians get through the busy streets of central London – rarely braking never mind stopping.