Scandal over Britain's failure to notify EU of crimes – an explainer

Jamie Grierson Home affairs correspondent
Photograph: Eva Plevier/Reuters

The UK failed to pass on the details of tens of thousands of foreign criminals to their home EU countries and concealed the scandal, the Guardian has learned. The police national computer (PNC) error went undetected for five years.

Related: Revealed: UK concealed failure to alert EU over 75,000 criminal convictions

What is the police national computer?

According to the College of Policing, the PNC is used to help investigations and sharing information of both national and local importance.

It provides critical services to the police, UK law enforcement and criminal justice agencies throughout the UK and it also links in with the European-wide IT system known as the Schengen Information System (SIS II) that enables all participating member states to share real-time information on persons and objects of interest via a series of alerts.

The PNC provides real-time checks on people, vehicles, crimes and property.

How does the PNC alert European partners?

The PNC generates daily activity files based on all the latest updates and any related to foreign offenders are meant to be forward to the European Criminal Records Information Exchange System (ECRIS) by a body known as ACRO Criminal Records Office.

What is ECRIS?

According to the European Union website, ECRIS was established in April 2012 to improve the exchange of information on criminal records throughout the EU. All EU countries are connected to ECRIS. The database ensures that information on convictions is exchanged between EU countries quickly and simply and provides judges and prosecutors with easy access to information on the criminal history of persons concerned. It also removes the possibility for offenders to escape convictions by moving from one EU country to another.

What is ACRO?

ACRO Criminal Records Office is a national police unit that provides a range of services to organise criminal records information and improve the links between criminal records and biometric information. It is also responsible for international police data sharing.

What has gone wrong with this system?

It has emerged that ACRO failed to pass on details of 75,000 convictions of foreign criminals to their home EU countries via ECRIS.

Why has this happened?

It appears to be a software glitch. ACRO has responded by developing a “software script” to fix the issue.

What are the implications of the error?

Dangerous foreign offenders once released from prison could return to their home countries without local authorities being aware of their presence.

How does this all fit into Brexit?

There have been warnings from law enforcement agencies about the impact Brexit could have on cross-border information sharing.

But this relates to an error with the domestic PNC, which ACRO is working to correct.

However, it has been revealed that the Home Office initially chose to conceal the embarrassing failure from EU partners.

It also follows revelations that the British authorities had made “unlawful” full or partial copies of the database that were said by an EU report to pose “serious and immediate risks to the integrity and security of SIS data”.

Both have served to undermine trust between the UK and the bloc.