Leading article: Who will police the police?

Scotland Yard is considering a criminal investigation into claims that journalists have been paying police officers for information.

This is a belated response to the 2003 admission by Rebekah Brooks, then a senior editor at Rupert Murdoch's News International media group, that her journalists have "paid the police for information in the past".

The matter is certainly worthy of investigation. If the police have been releasing sensitive information to journalists, in return for payment, that would meet most people's definition of corruption. And this is a particularly insidious crime because it undermines faith in the police, in whom the power of enforcing the law has been entrusted. Ms Brooks, who has since risen to become the chief executive of News International, tried to backtrack this week, saying she does not have information about specific payments. But there are plenty of other good reasons to believe that this has been widespread. The former News of the World journalist Paul McMullan alleges that a fifth of Metropolitan Police officers have taken backhanders from tabloid journalists for information.

Yet the idea that Scotland Yard should be in charge of this investigation – or should decide whether there are grounds for a probe – is surely a bad joke. It is inappropriate enough that the Metropolitan Police is investigating News International over the separate News of the World phone-hacking scandal after the force's lamentable (and suspicious) failure to do the job properly the first time around in 2006. But the notion that Scotland Yard can be trusted to investigate itself directly over corrupt dealings with tabloid journalists is even more ludicrous. An outside police force must be called in to conduct this probe.

There are very few organisations that, if accused of serious wrongdoing, would look credible if they volunteered to investigate themselves. And, after everything we have learned in recent months, the Metropolitan Police certainly cannot be counted among their number.