THE biggest police force in Europe was last night without a leader and Britain without its most senior counter-terrorism officer after Metropolitan Police Commissioner Paul Stephenson was followed out the door by Assistant Commissioner John Yates.

Sir Paul resigned early yesterday over allegations of an inappropriate relationship with former News of the World deputy editor Neil Wallis. He said speculation over his links to Mr Wallis had become a “distraction”.

Mr Yates resigned late last night after being told by the police watchdog that he would be suspended pending an investigation of his relationship with Mr Wallis.

He made a decision two years ago to not reopen police inquiries into phone hacking, saying he did not believe there was any new evidence to consider.

The resignation of the officer once touted as a successor to Sir Paul at Scotland Yard means Britain is without its most senior counter-terrorism official a year out from the London Olympics.

London Mayor Boris Johnson who praised Sir Paul after his resignation, said last night that Mr Yates’s departure was regrettable but the “right call”.

The resignations followed the defunct tabloid’s former editor Rebekah Brooks, who quit at News International chief executive on Friday, being questioned by police for 12 hours over the phone hacking scandal.

Ms Brooks was released yesterday morning on bail until October. She had attended a London police station by appointment almost 12 hours before, expecting to be interviewed as a witness, and was said to have been surprised at being taken into custody.

As well as facing questions over phone hacking, as part of Operation Weeting, Ms Brooks, 43, was interviewed in relation to Operation Eleveden, which is probing allegations that police gave information to journalists in exchange for illegal payments. In 2003, she told a Commons committee payments had been made to police.

Her spokesman David Wilson said her arrest would make her appearance at tonight’s session of the Commons culture, media and sport committee “pretty tricky”. It put her in an “invidious position” and she would seek legal advice on whether to attend.

The timing of the arrest two days before the session prompted some newspapers to hint at a deliberate hobbling of the parliamentary investigation.

Sir Paul is still expected to front the select committee tonight.

His resignation leaves the force without an obvious successor and puts Scotland Yard in the uncomfortable position of leading the widening probe into phone hacking and alleged police corruption even as its most senior official becomes a casualty of the case.

Mr Yates was last night recalled by the Commons home affairs committee to “clarify” tonight evidence he gave last week in light of Sir Paul’s resignation.

The metropolitan force had been under pressure over the awarding of a £24,000 public relations contract to Mr Wallis, who was arrested last week as part of Scotland Yard’s new probe into phone hacking.

In what appeared to be a parting shot at Prime Minister David Cameron, Sir Paul noted that unlike former NOTW editor Andy Coulson, Mr Cameron’s former communications chief, Mr Wallis had not left the newspaper under a cloud.

Sir Paul’s exit is unlikely to relieve pressure on the police force, with emails turned over by News Corporation to police last month suggesting some Met officers had taken bribes, and with the list of hacking victims now numbering 4000.

Scrutiny intensified at the weekend after revelations Sir Paul accepted £12,000 hospitality at a health retreat for which Mr Wallis was in charge of publicity.

The Met’s reputation was already damaged by its failure to properly investigate alleged illegal activities at the NOTW and by a perception that senior officers were too close to News International executives. “This is not a 12 months that can afford any doubts about the commissioner of the Met,” Sir Paul said.

He remained defiant, however, saying his integrity was “completely intact” and denied any impropriety over his stay at the Champney’s spa.

Mr Cameron said he understood Sir Paul’s decision but opposition home secretary spokeswoman Yvette Cooper said it was “striking” that Sir Paul had taken responsibility for the appointment of Mr Wallis, while Mr Cameron would not do so for appointing Mr Coulson as his media manager.