Andreas Whittam Smith: Can the reputation of the Met survive such a high-level duel?

While the Metropolitan Police investigates allegations of phone-hacking by journalists on the News of the World, its handling of the case is being challenged. The first inquiry is being conducted along conventional lines and has resulted in the arrests this week of the newspaper's chief reporter, Neville Thurlbeck, and of its former assistant editor, Ian Edmondson. They were both later released without charge on police bail.

Two parliamentary committees, Home Affairs and Culture, Media & Sport, are leading the second investigation. Essentially the charge against Scotland Yard is one of corruption. The suspicion is that it has been dilatory in investigating the News of the World because of an improper relationship with the newspaper. There may be many reasons for this, if it is so, including the close relationship between the ultimate boss of the News of the World, Rupert Murdoch, and successive prime ministers and the effect such cosiness may have had on the police.

Leaving aside speculation of this kind, there is one prime piece of evidence. This is the statement made by Rebekah Brooks in 2003 when she was editor of The Sun newspaper, also controlled by Mr Murdoch. She told the Home Affairs Select Committee: "We have paid police for information in the past." Was the Metropolitan Police Service involved? Now, 11 years later, Ms Brooks has been asked to provide details.

Pause here before we plunge into the legal points upon which the second case is turning. If a newspaper pays the police for information, it undermines the rule of law in two ways. Police investigations may be distorted because officers in receipt of payments are tempted to "improve" evidence in order to increase their earnings. At the same time, newspaper revelations of the progress of cases under investigation may prejudice a fair trial.

As if to emphasise the exceptional importance of the two actions – the one concerning the alleged prevalence of criminal activities in the way a national newspaper goes about its business and the second about the probity of the capital's police force – we are being treated to the remarkable spectacle of a duel between two senior officials: John Yates, head of counter-terrorism at Scotland Yard and acting Deputy Commissioner, and Keir Starmer QC, Director of Public Prosecutions and head of the Crown Prosecution Service. The weapons of choice are letters to parliamentary committees.

Mr Yates argues that the restrictive nature of the law explains why the results of the police investigation have been limited despite the large number of celebrities who claim to have been subject to phone-hacking. Under the Regulation of Investigatory Powers Act, in order to prove the offence of interception of a communication, it has to be shown, he says, that a voicemail had been intercepted prior to its being listened to by the intended recipient. The surprising contention is that the communication ceases to be such for the purposes of the Act once the message has been heard. In fact considerable expertise is required to establish whether a message has been listened to or not before it is subject to "hacking". As a result, states Mr Yates, we could only prove the offence in "a very small number of cases". The problem with this is that so far as the targets of the hacking are concerned, their privacy has been invaded either way.

Mr Yates goes on to argue that naturally the police did not arrive at this interpretation of the law all by themselves. The Crown Prosecution Service advised Scotland Yard every step of the way. It was from Mr Starmer's predecessor and his colleagues that the police learnt how difficult were the tests that must be met to secure a successful prosecution. The Yard had behaved properly throughout the case.

No, says Mr Starmer, that explanation is far too partial, while some MPs go further and say it is misleading. For Scotland Yard was told, Mr Starmer says, that the question of whether the Regulation of Investigatory Powers Act only relates to such messages that had not previously been accessed by the recipient was an area of the law that was "very much untested". Moreover, states Mr Starmer, if you examine the wording of the indictments in the two cases that were successfully prosecuted, you find that no reference was made to the timing issue. The police, advised by the Crown Prosecution Service, pragmatically decided to go ahead.

At this point in the duel, it seems to me, Mr Yates is losing ground. And then Mr Starmer comes in with two aggressive lunges. He says that the Met Police were told from the beginning that there were two other Acts under which they could bring prosecutions that did not run into timing difficulties. One is the Computer Misuse Act of 1990. This does not require knowledge of whether a message was hacked into before or after the recipient had heard it. And in addition, wrote a CPS official to Scotland Yard in 2006, "I would also be looking at considering an offence of conspiracy to commit those offences on the basis of other evidence being available". This approach would also avoid the "before" or "after" issue.

We shall have to wait to see how Mr Yates responds to these cuts and thrusts from Mr Starmer. There is probably also a long way to go in Scotland Yard's renewed inquiry into alleged phone-hacking by journalists. Yet already what is at stake is becoming clear.

First there is the reputation of national newspapers. It would be a serious matter if readers' suspicions that dubious practices extend far and wide were to receive confirmation from the phone-hacking inquiries. Then there is Mr Murdoch, who has just had his 80th birthday. He is one of the most successful media owners of the past 50 years. But if widespread criminality were to be revealed at one of his newspapers, that would be a poor way of concluding an illustrious career. Finally there is the Metropolitan Police Service. Its own performance is often an issue, as we see with the current inquiry into the policing of the G20 protests. Hardly a day goes by without some account of its failings being published. We really don't want to find that Mr Yates, whose main task is to head the Yard's counter-terrorism activities, must leave the service under a cloud.

a.whittamsmith@independent.co.uk