Tens of thousands of foreign criminals could be slipping through the net because police only check the backgrounds of one in seven, an official review revealed.
Of the tens of thousands of EU suspects arrested in the UK, officers only ask their home nation for a criminal record check in 15 per cent of cases, it emerged in a Home Office report.
In the courts last year alone, some 35,000 EU citizens were convicted but previous foreign offences were only sought from the Central Authority for the Exchange of Criminal Records (UKCA) in 5,500 cases.
It means in the majority of cases judges do not know the full offending history of tens of thousands of criminals when passing sentence.
Thousands more could have slipped under the radar if they were only arrested for a minor offence or not charged.
The report, for the Home Office, raised the prospect that foreign criminals could be working in sensitive positions or with children without their employers knowing their true past.
And Sunita Mason, who carried out the review of criminal record checks, warned that funding cuts to the UKCA could make the problem worse and pose a "potentially huge" risk to the public.
Mrs Mason said checks on EU citizens were "patchy" at best while those on people from outside Europe were "much less positive".
She said the problem of obtaining overseas convictions was "an ever-growing gulf of public protection".
She added: "In a world with far more global travel, both for work and pleasure, and with the less scrupulous taking advantage of these new opportunities to continue their offending behaviour across borders, it is clearly important that an individual's criminal record should include court convictions from other jurisdictions were possible."
Difficulty in obtaining such records means public protection agencies may not know the dangers posed by those they come in to contact with, she said.
The report also revealed that hundreds of previously unknown serious violent and sex offences committed by Britons while abroad have been unearthed.
The UK set up the UKCA in 2006 to improve the obtaining of criminal records from around the EU.
Since then, the agency has received 20,000 notifications of which 450 involved serious sex or violent offences committed by Britons overseas.
Only 37 of them were previously known while 276 involved offences against children.
However, Mrs Mason said funding for the agency over the next three years was unclear.
She warned: "Not to address this issue is a potentially huge public protection risk."
The report also said more work should be done to increase the number of occasions when fingerprints are also sent along with previous convictions to stop offenders turning up in the UK and claiming to be someone else.
It also recommended that potential employers should be allowed to request a foreign background check if the applicant agreed.
In January it emerged that more than one million crimes, including murders and rapes, are not on the Police National Computer because forces are refusing to pay a fee to obtain the criminal history of offenders.
A fifth of all crimes committed before 1995 are not on the national database because police must pay "100 to access each one from microfiche."
A Home Office spokeswoman said: "It is an operational matter for police to decide when to request information on foreign nationals.
"The UK worked hard to implement an EU-wide agreement to share this information - but we know all countries do not currently comply fully."
"That is why it is important that the new European legislation implemented next Spring will require member-states to share this information."
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