In correspondence with the House of Lords EU Committee, it said Croatia, Finland, France, Germany, Greece, Latvia, Poland, Slovakia, Slovenia and Sweden will be “invoking constitutional rules as reason not to extradite their own nationals to the UK”.
A letter from the Home Office said it amounted to “an absolute bar on the extradition of own nationals” to the UK.
Additionally, Austria and the Czech Republic will only extradite their own nationals to Britain with their consent.
It means that British authorities may have to attempt prosecutions in other countries, or circulate wanted criminals on an Interpol database in the hope they leave their home nation and can be caught elsewhere.
The UK was previously part of the European Arrest Warrant system, which allows a streamlined extradition process between EU states and has been used for high-profile terrorists, drug smugglers and murderers.
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As part of its post-Brexit security agreement, the UK has drawn up new extradition processes, but they do not have the same power to bypass constitutional barriers.
EU states can also refuse to surrender suspected criminals if the alleged offence does not exist in their country, or it is a “political” crime.
Richard Martin, the National Police Chiefs’ Council (NPCC) lead on Brexit planning, previously told the Home Affairs Committee that a new national extradition unit was formed in December.
He said that where countries refuse to extradite suspects, police have two choices: “One is we work with the Crown Prosecution Service and decide whether it is in the public interest to try and prosecute these individuals in their home countries.
“The second is we circulate them anyway on Interpol because as soon as they enter another country they’re fair game, so we can arrest them in that country and bring them back.”
A report published by the Lords EU Committee on Friday said the new extradition arrangements were “untested” and that their “operational effectiveness” should be scrutinised.
Peers also raised concern over the capability of the EU to terminate security cooperation over data protection rules and human rights.
Committee chair Lord Ricketts, a former national security adviser, said that although the agreement had avoided a feared “cliff-edge” for law enforcement, there were “still grounds for considerable caution”.
“These are a complex and untested set of arrangements and their effectiveness will depend crucially on how they are implemented at the operational level,” he added.
“The provisions on data protection are particularly fragile. If the UK does not remain in step with changes to EU data protection laws, or if the UK is found to have breached fundamental rights when handling personal data, then this could trigger the suspension, or even termination, of all the justice and security cooperation.”
The report said that the EU will continue to monitor UK data protection rules, and hold it to “higher standards” as a country outside the EU.
Peers warned that the situation increases the scope for legal challenges, which could trigger a suspension of the security agreement.
The document states that it can be terminated by either the UK or EU with nine months’ notice, for reasons including derogation from the European Convention on Human Rights (ECHR).
It is enshrined in British law through the Human Rights Act - but that is currently under review.
The law enforcement part of the Trade and Cooperation Agreement allows the continued sharing of policing and criminal justice data, including on DNA, fingerprints, air passenger information and criminal records.
But the UK lost access to the EU Schengen Information System (SIS II) database, which was previously integrated with the Police National Computer and searched more than 600 million times a year.
The Lords EU Committee report called the change the “most significant gap in terms of lost capability”, adding: “It means that, for the time being, law enforcement officers can no longer immediately have access to real-time data about persons and objects of interest, including wanted and missing persons.
“The fallback system, the Interpol I-24/7 database, currently provides data in a matter of hours, not seconds.”
Peers said that its success “depends heavily” on EU states accepting the additional workload of ‘double-keying’ data into both the SIS II and Interpol systems.
“We did not receive any clear evidence from the government on how it planned to secure such commitments from EU member states to do so,” the report said.
“We therefore remain concerned about the effect of the loss of access to SIS II on the operational effectiveness of UK police and law enforcement agencies.”
Kevin Foster, a Home Office minister, said the security agreement includes streamlined extradition arrangements.
“We continue to work closely with domestic and EU partners to monitor the new arrangements and have excellent cooperation with EU member states on a wide range of law enforcement and criminal justice issues,” he added.
“Some EU member states have long-held constitutional bars against the extradition of their own nationals to non-EU countries, which is why we negotiated a specific agreement which allows for offenders to face justice via another route, even where a country will not extradite their own national.”
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