The point isn't the "arrest" part (which doesn't mean what you think, actually -- they can, in fact, be arrested and charged for serious crimes while serving, a

The point isn't the "arrest" part (which doesn't mean what you think, actually -- they can, in fact, be arrested and charged for serious crimes while serving, and have been), it's the totality of the clause and its history, which acts to protect and caution against the criminalization or suppression of political activity. It's not a straightjacket, but more a statement of principle and warning shot. Edit: By the way, see http://en.wikipedia.org/wiki/Parliamentary_privilege http://en.wikipedia.org/wiki/Parliamentary_privilege