Evidence given by John Yates, the Metropolitan police assistant commissioner, to the home affairs select committee left a number of unanswered questions about his handling of the phone-hacking investigation.

His actions in July 2009

On 9 July 2009, the Guardian published a story that revived the hacking affair. Later that day, Yates announced that there were no grounds to reopen the original inquiry and said the News of the World's hacking had had few victims. There are several difficulties with this.

Yates was asked by the commissioner to "establish the facts". It is clear that he failed to do so. On Tuesday, he conceded that he had spent only eight hours doing so; that he had not spoken to Andy Hayman, the former assistant commissioner who oversaw the original inquiry; nor to Peter Clarke, the former deputy assistant commissioner who ran it; nor had he taken any legal advice; nor had he examined the contents of the material seized from the News of the World's investigator, Glenn Mulcaire, in August 2006. This is now known to include 11,000 pages of Mulcaire's hand-written notes, computer records and tape recordings of intercepted messages.

Yates' statement itself appears to be misleading. If he had not established the facts, he was in no position to judge whether or not the inquiry should be reopened, nor to make public any conclusion about the number of people who had been victims.

His current defence of that statement does not appear to hold water. He says his task was simply "to establish the facts about the Guardian article. Is there anything new we are not aware of? The plain fact is that there was not."

If the Met police did not know the contents of the seized material, then the Guardian article was indeed telling them new things that they were not aware of – for example, that there were thousands of victims, and that the former deputy prime minister John Prescott was among those targeted.

If, on the other hand, the Met police did know the contents of the seized material, then Yates had no basis for saying there were very few victims and claiming there was no evidence that Prescott had been hacked.

His actions in September 2010

On 1 September, the New York Times published an article with quotes from two former News of the World journalists – one named, one anonymous – which clearly indicated that hacking was widespread and well-known at the paper. Amid a political storm, Yates agreed to look at new evidence to see if it justified any further prosecution. Again, he has a series of difficulties.

First, it is difficult to understand why, knowing that Scotland Yard had a mass of material seized from Mulcaire and knowing this had never been properly searched, he ruled that only "new" evidence should be explored. The current inquiry, Operation Weeting, has since found numerous leads about previously unidentified victims and alleged perpetrators in this material.

Second, the detectives who interviewed the few journalists willing to give evidence insisted on treating them as suspects, not as witnesses, warning them that anything they said might be used in evidence against them. Sean Hoare, who had been willing to speak, then refused to answer questions. Another, Paul McMullan, challenged them to arrest him if they wanted to treat him as a suspect. The Crown Prosecution Service later concluded this inquiry had found no new evidence to justify any prosecution.

Yates has admitted that during this time, he continued to have social meetings with senior journalists from the News of the World, but he told the committee that this was acceptable because "I have never investigated these matters. They have come under my oversight, but there has never been an investigation that I have led." He describes the inquiries following the New York Times story as "a scoping study", not an investigation. He did not refer to the fact that the detective who led this operation was his own staff officer, Det Supt Dean Hayden.

Mobile phone companies

In September last year, Yates told the home affairs committee that police had "ensured" that mobile phone companies had warned all customers who had been identified as victims of hacking. In May this year, witnesses from the phone companies confirmed to the committee a Guardian disclosure that, in fact, none of them had been told to warn victims among their customers. All but one had followed normal protocol and kept their findings confidential because of the police inquiries.

Yates told the committee there was "a range of correspondence" between police and the phone companies. "In retrospect, it may not have been followed through in the way that it should have been," he said.

Legal advice from the Crown Prosecution Service

On four occasions, Yates has told parliament that prosecutors told police in 2006 that they must adopt a narrow interpretation of the law: that they needed to prove not only that voicemail had been intercepted but also that this had been done before the message had been heard by its intended recipient. He referred to this again on Tuesday. This is important because Yates has used this to justify his claim that the original inquiry found only 10 or 12 victims of hacking.

The current director of public prosecutions, Keir Starmer, has told the committee that, at an early stage of the original inquiry, an in-house lawyer at the CPS did raise this interpretation but added that it was "very much untested, and further consideration will need to be given to this". Later, according to Starmer, a senior barrister was appointed to run the prosecution and "he is clear that he did not at any stage give a definitive view that the narrow interpretation was the only possible interpretation". Yates, by contrast, earlier this year told the committee that the advice to adopt the narrow interpretation was "unequivocal".