What do you do when Her Majesty or the PM walk through the door?

You know who always make the news for appearing at church services during Christmas and Easter?
The British Royal Family and, to a lesser degree, the top politicians in Australia.

How do churches, especially those preaching, react to these "special guests?"

Do they know in advance?
If so, do they proceed as usual?
If not, do they freak out when HRH appears?

Do they slink away from controversial points?
Or, do they hit controversial topics harder due to the influential ears listening?

Do they ramp up the idea of the sovereignty of God?
Do they go out of their way to especially mention the kingship/lordship of Jesus?

Do they avoid readings which deal with leadership or the government, even if they are, by pure coincidence, in the lectionary?

I've never had, from what I remember, a "celebrity" in attendance when I've preached, nor attended at church with a person of significant influence, but I'd hope that everything would proceed as normal.

Unfortunately, I also doubt that I'd be either a) that self controlled, or b) that strong-willed.