Walking down Upper Street yesterday afternoon at four I passed the Prime Minister going the other way. To the summit in Watford, presumably. I've seen the PM's motorcade on a few occasions. There are police cars fore and aft but the main body consists of two black Range Rovers and two black Jags. I suppose the idea is that the potential assassin doesn't know which one contains the target.
It's nothing compared to the American President. I was in Sydney, Australia when Clinton was visiting and everywhere I went in that quite small city my progress was held up by his endless motorcade, plasma trucks and all. I eventually gave up and returned to my hotel room overlooking the harbour. I opened the curtains just in time to see Clinton and John Howard's boat pushing off from the adjacent dock. Looking around for someone to wave at, they waved at the only available person, which was me. I waved back.
A few years later I was passing through Green Park on a summer's evening and made to cross the Mall just as a limo bearing the royal standard came off the roundabout in front of Buckingham Palace. I was the only pedestrian on the Mall as the car went slowly past me. The passengers were the Queen and Prince Philip. They waved. I waved back.