You might say it was a brave move for Acting Deputy Commissioner John Yates to ask to be questioned in public again by MPs about the phone hacking scandal. He clearly feels stung by the suggestion — put forward most recently by Chris Bryant MP in Parliament — that he misled the Commons media committee on the subject in 2009.

Yates’s justification then for implying that the News of the World’s hacking was a small-scale affair rests on a legal point — he says the Crown Prosecution Service told the Met to stick to a very narrow definition of the offence, and so officers acted accordingly. The CPS, however, tells the story differently.

No doubt Yates has some answers on all that; he would be a fool if he didn’t. It will be of greater long-term interest, however, to see how he responds to questioning about other aspects of the Met’s conduct in the hacking affair, because he won’t escape without that.

I saw his performance in 2009 and I recall thinking that if I was a serious criminal under investigation I would want Yates to be in charge of my case. For a top detective he seemed astonishingly unsuspicious. Police knew that a News of the World reporter transcribed dozens of voicemails, but they never questioned the reporter or the person whose phone had been hacked. The transcripts were marked “for Neville”, but police never established who that was, even though the paper employed only one person called Neville, and he was the chief reporter. And so on.

Yates insisted there was nothing wrong with all this myopia. I have written before that one of the most remarkable characteristics of the whole phone hacking affair is that people keep saying utterly incredible things and expecting you to believe them. So police officers can’t spot a lead that would have been obvious to an Enid Blyton reader and the entire staff of a national newspaper can’t remember a single thing about a story (about Gordon Taylor) which they fully intended to put on their own front page.

Yates will be questioned in detail this week about why the Met kept insisting there were very few hacking victims. Just as important, however, is the matter of how the police have handled inquiries from possible victims who have asked them about evidence. Lawyers have been lining up to complain that these inquiries were frequently stalled and even obstructed by police, in a way that has benefited one party — Rupert Murdoch’s News International. Why was that?

There is the matter of when the police studied and audited the voluminous hacking information they seized in 2006. Read Yates’s evidence from 2009 and you would probably form the impression that his officers were on top of it, that they had seen every piece of paper and every computer file and they knew its evidential significance. That position, however, is difficult to reconcile with our present knowledge — see for example the case now being made on behalf of Sienna Miller. It is also difficult to reconcile with the fact that the Met has launched a new, “robust” investigation into the whole affair.

There is much more. Why did three years pass before we learned that the princes, William and Harry, were victims? (That delay benefited News International by muting the public outcry.) If the documents offered the slightest hint that John Prescott, then deputy prime minister, had been hacked by a private investigator, why was the matter not pursued with the utmost vigour, as an issue of national security? Why did the Met tiptoe into the News of the World office in August 2006 and seize only the barest minimum of their materials? Why did Met officers dine with News International executives at a time when the company was under investigation? Has the Met investigated whether any police officers helped Glenn Mulcaire gain his industrial-scale access to mobile phone data?

There is a lot to address, besides the matter of the CPS’s legal advice. Yates may need to remind himself, as he sits there facing the music for his force, that he asked for it.

Brian Cathcart teaches journalism at Kingston University London. Follow him on Twitter: @BrianCathcart