Britain's largest police force has been rebuked by a watchdog over its use of a controversial database set up to tackle gang crime.
An investigation by the Information Commissioner's Office (ICO) concluded the Metropolitan Police committed multiple and serious breaches of data protection laws.
The findings relate to the Gangs Matrix, which is used to record intelligence related to alleged gang members.
Details logged on the database include full names, dates of birth, home addresses, and information on whether someone is a prolific firearms offender or knife carrier.
The model aims to help officers take enforcement action using an "Al Capone approach" where prosecution for specific gang-related crimes is not possible.
But the scheme has come under fire and the ICO launched a probe in October last year after concerns were raised by Amnesty International.
The investigation concluded that, while there was a valid purpose for the database, the inconsistent way it was being used did not comply with data protection rules.
The ICO found:
The Gangs Matrix does not clearly distinguish between the approach to victims of gang-related crime and perpetrators;
Some boroughs operated informal lists of people who had been removed from the Gangs Matrix, meaning the Met continued to monitor individuals even when intelligence had shown they were no longer active gang members;
Excessive processing of data as a result of blanket sharing with third parties failed to distinguish between those assessed as high-risk and low risk, with the potential for disproportionate action to be taken against people no longer posing a risk;
Serious breaches of data protection laws had the potential to cause damage and distress to the disproportionate number of young, black men on the Matrix;
There was an absence of effective central governance, oversight or audit of data processed and a failure to ensure a consistent approach to the relevance of social media information;
Gangs Matrix data was routinely transferred in a variety of unsecured ways.
The "very serious" contraventions date back to 2011 and have affected a "significant number" of data subjects including children and vulnerable individuals, the ICO found.
However, it decided against ordering the force to cease processing data through the Gangs Matrix altogether.
The watchdog has issued an enforcement notice which requires the Met to take a number of steps within six months.
Deputy Information Commissioner of Operations James Dipple-Johnstone said: "Protecting the public from violent crime is an important mission and we recognise the unique challenges the MPS (Metropolitan Police Service) faces in tackling this.
"Our aim is not to prevent this vital work, nor are we saying that the use of a database in this context is not appropriate; we need to ensure that there are suitable policies and processes in place and that these are followed.
"Clear and rigorous oversight and governance is essential, so the personal data of people on the database is protected and the community can have confidence that their information is being used in an appropriate way."
The ICO noted the Met already has an action plan under way and has committed to bringing the Gangs Matrix in line with data protection laws.
It has also stopped sharing data with third parties where there is no individual sharing agreement in place.
Amnesty International's technology director Tanya O'Carrol said the investigation confirms the Gangs Matrix is "currently not fit for purpose".
Deputy Assistant Commissioner for Met Operations Duncan Ball said the force will continue using the Gangs Matrix in its work to reduce the impact of gang violence and bring safety to communities.
He added: "We have already started work to ensure that we improve our data handling and information sharing with partners, who are also involved in community safety work.
"As well as addressing the concerns within the ICO report, we are also taking forward additional work including the introduction of a public facing website to explain the legal framework for the Gangs Matrix and further information to improve public confidence and transparency."