Gentlemen, start your engines

I decided to schlep over to Buckingham Palace at lunchtime. Something was happening, as it often does, but I am not sure what the something was. I have narrowed it down to:

1) They were waiting for someone royal or an important person to escort off the premises - but I waited over 20 seconds and nothing happened, so unlikely.

2) This was the only parking space available in central London - the police tend to park anywhere (I cycled round a police van parked in the middle of a bus lane yesterday - no one about), so probably not the reason.

3) They were waiting to start the Palace GP:10 circuits of the Palace forecourt, first home wins (no bumping, grinding, or smiling allowed) - they were all revved up and ready to go, so this is the most likely explanation.

Incidentally, this lot were out-and-about again, playing a rather pleasant tune. I hope they got back in time for their lunch.