Sir Paul Stephenson, the head of the Metropolitan police -- and Britain's most senior police officer -- has resigned. He said that he had "taken this decision as a consequence of ongoing speculation and accusations relating to the Met's links with News International".

Earlier in the day, former NI chief executive Rebekah Brooks was arrested by officers of Operation Weeting - the hacking enquiry - and Operation Elveden, which is investigating allegations of improper payments to police.

In the Sunday newspapers, Sir Paul had come under fire over the employment of former News of the World executive Neil Wallis in 2009 as a PR adviser to the Met. Wallis was arrested by Operation Weeting last week.

Stephenson said that he had not revealed his links to Wallis because he did not want to "compromise" David Cameron, who had employed Wallis's boss at the News of the World, Andy Coulson:

Once Mr Wallis's name did become associated with Operation Weeting, I did not want to compromise the Prime Minister in any way by revealing or discussing a potential suspect who clearly had a close relationship with Mr Coulson. I am aware of the many political exchanges in relation to Mr Coulson's previous employment - I believe it would have been extraordinarily clumsy of me to have exposed the Prime Minister, or by association the Home Secretary, to any accusation, however unfair, as a consequence of them being in possession of operational information in this regard. Similarly, the Mayor. Because of the individuals involved, their positions and relationships, these were I believe unique circumstances.

The Guardian's editor, Alan Rusbridger [2], said one colleague had described this paragraph as "a hand grenade lobbed at Downing Street", although there could also be an innocent explanation.

Keith Vaz MP told the BBC News Channel he was "genuinely shocked" by the resignation, particularly since Stephenson is due to give evidence to the Culture, Media and Sport Select Committee on Tuesday.

Rebekah Brooks is also due to give evidence at the committee, although it is unclear whether she will now appear.

London Mayor Boris Johnson said he was "very reluctant" to accept the resignation, as Stephenson was "widely admired". "The so-called nexus between the News of the World and the Met was going to make life difficult . . . he didn't want to have that kind of distraction," said Johnson.

Here is the text of Stephenson's resignation statement [3]:

I have taken this decision as a consequence of the ongoing speculation and accusations relating to the Met's links with News International at a senior level and in particular in relation to Mr Neil Wallis who as you know was arrested in connection with Operation Weeting last week.
...

Let me turn to phone hacking and my relationship with Neil Wallis. I want to put the record straight.
I met Mr Wallis in 2006. The purpose of that meeting was, as with other journalists, to represent the context of policing and to better inform the public debate carried out through the media on policing issues.
I had no knowledge of, or involvement in, the original investigation into phone hacking in 2006 that successfully led to the conviction and imprisonment of two men. I had no reason to believe this was anything other than a successful investigation. I was unaware that there were any other documents in our possession of the nature that have now emerged.
I have acknowledged the statement by John Yates that if he had known then what he knows now he would have made different decisions.
My relationship with Mr Wallis continued over the following years and the frequency of our meetings is a matter of public record. The record clearly accords with my description of the relationship as one maintained for professional purposes and an acquaintance.
In 2009 the Met entered into a contractual arrangement with Neil Wallis, terminating in 2010. I played no role in the letting or management of that contract.
I have heard suggestions that we must have suspected the alleged involvement of Mr Wallis in phone hacking. Let me say unequivocally that I did not and had no reason to have done so. I do not occupy a position in the world of journalism; I had no knowledge of the extent of this disgraceful practice and the repugnant nature of the selection of victims that is now emerging; nor of its apparent reach into senior levels.

The full statement can be found at Channel 4 News [4].