Police officers with the country's largest force have been caught assisting criminals, selling confidential details for cash and making racist and sexist comments on the internet, a Press Association investigation has found.
Others within the Metropolitan Police harassed colleagues, bragged about their law breaking and lied to managers in an effort to cover up breaches of Data Protection rules.
The results of the investigation, which show 300 police breaches during nearly five years, have prompted calls for the Met to carry out an urgent review of its security procedures, while civil liberties campaigners want changes to legislation allowing greater penalties for those who break rules.
A force spokesman said it demands all employees "act with professionalism and integrity whether on or off-duty", and comply with rules.
The Data Protection breaches are the latest embarrassment to the Met, after investigations by national newspapers discovered corruption within the force, while a damning report by barrister Mark Ellison QC found that an undercover officer was a "spy" within the "family camp" of murdered black teenager Stephen Lawrence.
Former shadow home secretary David Davis said the breaches undermined public trust in the police.
The Tory MP for Haltemprice and Howden said: "The extent to which police officers have used confidential police information for criminal ends, and abused individuals' private information for their personal benefit, is astonishing.
"This directly impacts on the level of trust between the police and the public.
"The public are much more shocked when it is vulnerable, ordinary people who are victimised rather than powerful celebrities. These revelations are the sort of thing that will deeply concern the man on the street.
"The Met needs to review, as a matter of urgency, the security control for confidential information that the police hold on members of the public."
The breaches cover rank-and-file officers, senior investigators and civilian staff at the Met, which employs around 31,000 officers,13,000 police staff and 2,600 Police Community Support Officers (PCSO).
Around one-fifth of cases ended in a sacking or retirement, while two-thirds resulted in formal action.
Breaches between January 2009 and October 2013 range from minor rule-breaks on social media to serious allegations of misconduct leading to arrests.
According to the Met, criminals used an officer to "obtain data from police indices to assist in criminality". The criminals had been subject to public protection arrangements usually reserved for sexual or violent offenders.
Another officer was arrested for leaking intelligence "of a significant level to a prominent criminal with links to firearms", the Met said.
A further officer was discovered to be passing on confidential information regarding drugs. In both cases, the employee was arrested and is no longer working for the force.
A detective chief inspector received formal action after committing "offences contrary to the Prevention of Corruption Act", the force said.
In a handful of cases, journalists were secretly supplied with information by police - sometimes in exchange for cash, the Met confirmed.
There were also occasions when employees were censured for posting offensive material on Facebook and for behaving inappropriately at work.
A police officer was reprimanded for making inappropriate sexual comments about children on a website, while another sent a spoof image of a caravan adorned with Nazi references to an external address.
A special constable received formal action for making the comment "damn n*****s" on a Facebook photo of two men fighting, while one officer received management action for sending a picture of armed police outside the Commons, captioned with the words "Merry Christmas... Keep calm and f**k off."
Another officer breached data laws after disclosing on Facebook that he had lost a bag containing police paper and equipment, while one employee joined the Facebook of Sex website and posted photos of himself.
An officer also used their internal email for dating purposes, some searched for pornography, while a PCSO used the police computer to check up on her boyfriend.
Another "s earched details of a cab driver he had refused to pay a few nights before".
Of the 300 cases investigated and substantiated, 208 were subject to formal action being taken - including criminal prosecutions where appropriate.
The remaining 92 cases resulted in a variety of outcomes including written warnings, management action, retirement or resignation (allowed by police regulations) and two cases of no further action.
Emma Carr, deputy director of civil liberties group Big Brother Watch, said police needed to be more transparent in coming clean about staff data breaches.
She said: " It shouldn't take journalists or campaign groups to ask for that information because it looks like they are hiding something.
"It's also important that police do their utmost to ensure people are disciplined when malicious data sharing has taken place, and for them to ensure that if criminality has occurred they feel the full force of the law - it shouldn't be one rule for police and one for the rest of us."
She added: "I think we have seen so many stories recently of potential corruption taking place within the police, with malicious practice or people not really sticking to the law that we're supposed to keep as the general public.
"When you then have other tensions taking place within communities, that's clearly going to add to mistrust between police forces and the public when you really need them to work together.
"That's why its important the heads of the police force are seen to be doing something to ensure they are running a clean unit."
A Met spokesman said: "We recognise that protecting the sensitive data we hold is critical to public confidence and our ability to fight crime effectively.
"The MPS treats any allegation about the conduct of its staff extremely seriously and will always take steps to determine whether the conduct of that member of staff has breached the required standards of professional behaviour."
Asked how public confidence would be affected by evidence of racism, the spokesman added: "The Commissioner has stated he will not tolerate racism and recognises that the Met needs to continuously improve. All staff are aware that racism will not be tolerated and this is made clear when they join and throughout their careers."