"Secret Policeman's Ball" joke

From London Times via Car and Driver:
Comrade Gorbachev is being driven from his dacha to Moscow and
is in a hurry. He is getting irritated with the slowness of his
driver. "Can't you go any faster?" he says angrily. "I have to
obey the speed limits," says the driver.
Finally Gorbachev
orders the driver into the back and takes the wheel. Sure
enough a patrol car soon pulls them over. The senior officer
orders the junior to go write up the ticket. But the junior
officer comes back and says he can't give them a ticket, the
person in the car is too important.
"Well, who is it?" the senior officer asks.
"I didn't recognize him," says the junior
officer, "but Comrade Gorbachev is his chauffeur."
Raj Wall
Texas Instruments