Magna Carta and today's remedy of Judicial Review.
But the State isn't the only source of threats to the rights of citizens. As Magna Carta sought to curb the excesses of a monarch, it didn't seek to curb the actions of 'over mighty subjects'. The Barons at Runnymede didn't want that issue addressed!
The phone-tapping scandal involving the News of the World (another part of Rupert Murdoch's global media empire); the damage to the livelihood of people affected bt the BP scandal; the ability of corporations to use their money to influence the political process - show that powerful business interests are a threat too.