Yvette Cooper MP, Labour's shadow home secretary, questions why different rules apply to the Met police commissioner and the prime minister over phone-hacking links:

"Sir Paul has taken a brave and honourable decision, putting the operational effectiveness of Metropolitan police officers above all else.

"He has done an excellent job in cutting crime in London and in policing national celebrations to large scale demonstrations. His operational pedigree is without question.

"Ultimately Sir Paul has taken responsibility for a saga which he makes clear in his statement he had no direct involvement with from the beginning, because of the continued speculation around the appointment of Neil Wallis.

"It is striking that Sir Paul has taken responsibility and answered questions about the appointment of the deputy editor of the News of the World whereas the prime minister still refuses to recognise his misjudgement and answer questions on the appointment of the editor of the News of the World at the time of the initial phone hacking investigation.

"People will wonder at why different rules apply for the prime minister and the Met, especially when as Sir Paul said himself, unlike Andy Coulson, Neil Wallis had not been forced to resign from the News of the World.

"It is also a very serious concern that the Met commissioner felt unable to tell the prime minister and the home secretary about this operational issue with Neil Wallis because of the prime minister's relationship with Andy Coulson. It appears that their compromised relationship with Andy Coulson has put the commissioner in a very difficult position and made it even harder for the Met to maintain confidence around this difficult issue. Both David Cameron and Theresa May must take their share of the responsibility for this situation."