Police officers in London have been caught assisting criminals by providing them with sensitive police information, it has been revealed.
According to the Metropolitan Police, criminals used an officer in one case 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.
One officer was discovered to be passing on confidential information regarding drugs. In both cases, the officer 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.
The Met's officers have also been caught selling confidential details for cash and making racist and sexist comments on the internet.
They harassed colleagues, bragged about their law breaking and lied to managers in an effort to cover up breaches of data protection rules.
The revelation that there were 300 such breaches during nearly five years, has prompted calls for the Met to review its security procedures, while civil liberties campaigners want changes to legislation allowing greater penalties for those who break rules.
Former shadow home secretary David Davis said the breaches undermined public trust in the police and were "astonishing".
He said: "The extent to which 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."
A force spokesman said it demands its workforce "act with professionalism and integrity whether on or off-duty", and comply with rules.
The breaches cover rank-and-file officers, senior investigators and staff, who do not have the power of arrest, which employs around 31,000 officers, 13,000 staff and 2,600 Police Community Support Officers (PCSOs).
Around one-fifth of cases ended with the individual leaving the force, 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.
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 fuck 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 "searched 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.
The remaining 92 cases resulted in a variety of outcomes including written warnings, management action, retirement or resignation and two cases of no further action.
A Met spokesman said: "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."
"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.