The UK's most senior officer, Sir Paul Stephenson, survived the first two major crises of his reign - the arrest of Conservative MP Damian Green and the student protests.
But he resigned without warning, as the Metropolitan police force became drawn ever closer into the phone hacking and corruption probes at the News of the World.
When claims that Met police officers had been paid by the newspaper surfaced publicly at the beginning of July, Sir Paul came out gunning.
He referred the force's internal investigation to the Independent Police Complains Commission (IPCC) and vowed to "root out" and put in front of a criminal court any corrupt staff.
Since then his own judgement as Met Commissioner has been questioned, a situation which could yet prove to be the most serious dilemma of his two-and-a-half year reign.
First it emerged that former News of the World executive Neil Wallis - who was questioned by police investigating phone hacking claims - had worked for the force as a media consultant.
Then it was reported that Sir Paul received hospitality from a Champneys health spa while recovering from the removal of a pre-cancerous tumour in his leg.
It is claimed that Mr Wallis was working as the public relations man for Champneys at the time - as well as for the Met.
Sir Paul, 57, admitted going to the spa but said he had no idea Mr Wallis worked for Champneys.
He said he accepted the gift because he was good friends personally, rather than professionally, with the managing director of the spa.
Politicians began asking questions and Home Secretary Theresa May was to address MPs about her "concerns".
Sir Paul's sudden resignation came on a Sunday evening, 17 July 2011, in a televised statement.
He said that his integrity was intact, but that his links with Mr Wallis could hamper current investigations.
Sir Paul, who became commissioner in January 2009, had been no stranger to the politics of the job.
He was in the firing line when the Met was criticised for what Conservatives said was a heavy-handed operation to combat Home Office leaks when officers arrested shadow immigration minister Damian Green.
Then in December last year, his force came under fire for security breaches which allowed protesters to attack a royal limousine carrying Prince Charles and the Duchess of Cornwall.
The son of a Lancashire butcher, he decided against university and followed his brother into the police, joining Lancashire Constabulary in 1975.
He rose rapidly, becoming a superintendent by 1988 followed by a spell in the then Royal Ulster Constabulary, a force which was still busy dealing with the threat of terrorism.
In 1994 he was appointed assistant chief constable of Merseyside with responsibility for territorial policing.
His profile on the Met police website said he took a leading role in reducing gun crime, anti-corruption and combating terrorism.
His most politically sensitive role came in 1996 when Parliament granted MI5 powers to look into serious and organised crime - something the Security Service had never previously done.
This led to Sir Paul leading negotiations on the working relationship between police officers and MI5 - a precursor to the joint counter-terrorism operations of today.
In 1999, he was appointed deputy chief constable of Lancashire and took the top job three years later.
During his time back at the force, he oversaw fundamental changes to the constabulary's working practices, designed to modernise the force in line with new thinking developed in the USA.
He also became the national spokesman for crime at the Association of Chief Police Officers.
While he was in charge, Lancashire was consistently in the "top tier" of police performance league tables.
In March 2005, he moved to London after being made the Met's deputy commissioner.
Four months later the 7 July attacks changed his role and that of his boss Sir Ian Blair.
Two weeks after the suicide bombings, Jean Charles de Menezes was mistakenly shot by officers in an attempt to foil a second suicide plot.
Sir Ian was eventually forced out by London Mayor Boris Johnson in 2008, paving the way for Sir Paul's appointment.
He beat Sir Hugh Orde, Chief Constable for Northern Ireland, into second place for the top job.
Known for his straight-talking manner and retaining his Lancashire accent, Sir Paul was nicknamed "Rusty" by some because of his frequently tanned face.
He was awarded the Queen's Police Medal in 2000 and knighted in the 2008 birthday honours.