Met Police Assistant Commissioner John Yates has quit after growing pressure amid the phone-hacking scandal.Mr Yates checked the credentials of Neil Wallis before the Met employed the former News of the World executive, arrested last week over hacking claims.
Mr Yates decided to resign after the Metropolitan Police Authority told him he was to be suspended. Commissioner Sir Paul Stephenson quit on Sunday.
London mayor Boris Johnson said it had been right for both men to stand down.
'Distracting questions' Mr Yates said in a statement that his conscience was clear and spoke of his "deep regret" over his resignation.
In other developments on Monday: The Independent Police Complaints Commission said it had received referrals from the Metropolitan Police Authority about the conduct of four current or former senior Met officers
Labour leader Ed Miliband again attacked Prime Minister David Cameron for hiring former News of the World editor Andy Coulson at Number 10
Former News International chief executive Rebekah Brooks confirmed she would appear before a committee of MPs on Tuesday, alongside Rupert and James Murdoch, despite her arrest and questioning by police on Sunday
News Corporation established an independent body headed by senior barrister Lord Grabiner QC to lead its internal inquiry into the News of the World phone-hacking scandal
Shares in News Corporation dropped by 7.6% to a two-year low in trading in Australia, and suffered a 4.3% fall in New York
The Serious Fraud Office said it would give "full consideration" to a request by Labour MP Tom Watson to investigate out-of-court settlements made to hacking victims
Press Association reporter Laura Elston will face no further action, her lawyer said. She had been arrested last month by police investigating allegations of phone hacking by journalists
The Mayor of London said Deputy Commissioner Tim Godwin would be in charge at Scotland Yard until Sir Paul's replacement was appointed. Mr Yates will be replaced in the interim as the Met's head of counter-terrorism by Assistant Commissioner Cressida Dick.
Mr Johnson told a news conference at City Hall in London: "There is absolutely nothing that has been proven against the probity or the professionalism of either man.
"But in both cases we have to recognise that the nexus of questions about the relationship between the Met and the News of the World was likely to be distracting to both officers in the run-up to the Olympic Games."
Home Secretary Theresa May said in a statement to MPs that she was "sorry" over Sir Paul's decision to resign and that the Met was "stronger operationally today than it was when he took over".
Ms May announced that HM Inspectorate of Constabulary would launch an inquiry into corruption in the police, and Independent Police Complaints Commission investigations on the same issue would be part of the judge-led inquiry into the hacking scandal.
Mr Cameron, who is on a trade visit to Africa, said: "John Yates was a well-respected detective, and has more recently provided strong leadership on counter-terrorism policing. What matters now is that we ensure swift and effective continuity at the Metropolitan Police Service."
The prime minister is cutting short his trip to prepare for a statement to the Commons on Wednesday. He earlier announced the recall of the Commons to debate the latest developments in the phone-hacking scandal.
'Lengthy deliberations' The resignation of Sir Paul, the most senior policeman in Britain, came after he faced criticism for the Met's recruitment of Mr Wallis as a PR consultant.
Mr Wallis, a former NoW deputy editor, was arrested and released on bail on Thursday on suspicion of conspiring to intercept communications.
- Cressida Dick, who has taken over John Yates's responsibilities as the Met's head of counter-terrorism, is said to be popular among rank-and-file officers, who rallied to her defence in the wake of the shooting of Jean Charles de Menezes
- She was the gold commander whose job it was to co-ordinate the attempts to catch the men behind the 21 July 2005 failed bombings
- When, in 2007, an Old Bailey jury found the Met guilty of endangering the public, they took the unusual step of declaring there was "no personal culpability for Commander Cressida Dick"
- She was born and brought up in Oxford, went to university there and graduated from Balliol College
- She started out in accountancy but switched careers in 1983 and worked her way up the ladder
- After a spell at Thames Valley Police, she was promoted to deputy assistant commissioner before becoming the first female assistant commissioner in 2009
The day after the commissioner's resignation, Mr Yates told Metropolitan Police Authority (MPA) chairman Kit Malthouse that he was also standing down.Scotland Yard said in a statement: "Assistant Commissioner John Yates has this afternoon indicated his intention to resign to the chair of the MPA. This has been accepted."
Mr Yates's resignation came after he was informed he would be suspended pending an inquiry into his relationship with Mr Wallis.
The officer had been confronted with new information about the friendship between the two men, sources told BBC political editor Nick Robinson.
After a meeting of the Metropolitan Police Authority's professional standards committee, the MPA said in a statement: "The committee considered allegations concerning Assistant Commissioner John Yates and after lengthy and careful deliberations decided to suspend the assistant commissioner.
"Suspension is not a disciplinary sanction and it is emphasised that suspension should not be taken as a presumption of guilt. Assistant Commissioner Yates has been informed of this decision.
"A number of matters have been referred to the Independent Police Complaints Commission, including one involving Assistant Commissioner Yates."