Under the right to freedom of speech, what one white person says to another in the form of a joke is their business and noone else's. They are not inciting racial hatred here, and far from it.
I know coppers, firemen, etc, so naturally as soon as anything happens, like 7/7, 21/7 the Brazillian shooting, the tsunami, I normally get jokes about it. I joked back to one, that'll get you sent to Belmarsh if Blair gets his way (reference to proposed terror laws).
Another side point, TB is still trying to get religious jokes banned.
Noone has to hear a joke, so if they do, it is their own responsibility if someone is offended by it.