Ah, but privacy is an essential part of liberty, and liberty is a right, not a privilege. I believe our countries had a disagreement about this a couple of hundred years ago. ;-)
Besides, we don't have to worry about MI5. We've got the NSA, CIA, FBI, and DHS all waging the battle against privacy. It is a big concern, which is why I think it would be highly beneficial for *all* email and VoIP data streams to be encrypted. It would still be possible to see that a conversation took place but it would not be possible to listen in on the conversation.