Leading article: A police force that has lost public trust

Perhaps the most disturbing aspect of the still unfolding phone-hacking scandal is the behaviour of the Metropolitan Police. Scotland Yard has pursued its investigations in a most lethargic and blinkered manner.

After the News of the World reporter Clive Goodman was jailed in 2007 for hacking into Prince William's mobile phone messages, Scotland Yard accepted, apparently without question, the assertion of the newspaper that Goodman was a single "rogue" operative. When allegations were made last September that the scale of the eavesdropping operation at the News of the World went considerably further, the police returned to their files and again concluded that there was no reason to re-open the case.

But this week Rupert Murdoch's News International group, the parent company of The News of the World, admitted that "significant new evidence" of wrongdoing by its staff had come to light. This not only contradicts News International's own previous categorical denials that hacking was endemic at the newspaper; it raises troubling questions about the thoroughness of Scotland Yard's investigations.

Two conclusions present themselves: either the police were incompetent or they were intent on turning a blind eye to illegality. It would be foolish to rule out incompetence where an organisation like Scotland Yard is involved. But wilful blindness in this instance seems the more likely explanation. There is a widespread suspicion that the police attempted to quash this investigation because of its cosy relationship with News International.

The Metropolitan Police's former assistant commissioner, Brian Paddick, has spoken of "a whole media machine at New Scotland Yard designed to try and make sure the police are portrayed positively in the media". And senior detectives have complained of coming under pressure internally not to push the case too hard. Scotland Yard's dilatory investigation certainly makes for a striking contrast with its zealous prosecution of the cash-for-honours inquiry in 2007.

If the police have tried to thwart this investigation the implications will be toxic. The public expect and demand that the police investigate allegations of malfeasance without fear, favour or partiality. The suspicion that they soft-pedalled an investigation into a powerful newspaper group risks undermining faith in the rule of law.

In the light of this week's developments, Scotland Yard is to launch yet another investigation into phone-hacking. This has been taken out of the hands of the deputy commissioner, John Yates, and given to deputy assistant commissioner, Sue Akers. The acting Metropolitan Police Commissioner, Tim Godwin, speaking at a meeting of the Metropolitan Police Authority yesterday, promised that the new investigation would "leave no stone unturned".

But it is too late for such fine words of resolve. The only way to restore trust in this investigation is to hand it over to an entirely different police force, one not compromised by links with Rupert Murdoch's media empire. A government that understood the importance of upholding the rule of law would have already ordered this. Yet all ministers have offered is silence. And the suspicion is growing that the Coalition itself is afraid of offending Mr Murdoch's mighty media empire.

Theresa May, the Home Secretary, needs to make a statement to the House of Commons on this investigation to lay to rest suspicions of secret understandings and special treatment. We need to be reassured that, in 21st century Britain, all are indeed equal under the law.