Mr Yates came under fierce questioning from MPs on the select committee over the police’s decision not to contact some 91 people – believed to include politicians and celebrities – whose voicemail PINs were discovered during the investigations into Goodman and Mulcaire.

He said that police or mobile phone service providers had contacted around 10 to 12 people in cases where they thought there was "the minutest possibility" that an attempt had been made to hack into their messages.

Mr Yates defended the initial police inquiry, telling MPs: "You may not believe it, but I still think the investigation was a success, and if HMI (the Inspector of Constabulary) wants to come and have a look at it, I wouldn’t have a problem at all."

The jailing of Goodman and Mulcaire had sent out a "very significant deterrent message" and the case had clarified the law relating to interception of communications, he said.

It was a "dangerous assumption" to believe that any particular individual named on lists seized during the police investigation was necessarily the victim of eavesdropping, he warned MPs.

Phone-hacking was very narrowly defined in legislation and was "very, very difficult to prove", he said.

Top barristers had advised police that obtaining a PIN without the owner’s permission was not in itself a crime, said Mr Yates.

But committee chairman Keith Vaz told him that this would be a breach of the Data Protection Act.

He urged him to contact all those whose details were found on Mulcaire’s lists: "They are the victims of crime in the same way as if someone’s bank account has been hacked into. You would write to those people and inform them."

Mr Vaz added: "I think it is the feeling of this committee that there are some questions which remain to be answered."