A potential clash is building between the EU and UK over the question of extraditing suspects from Britain to EU member states post-Brexit.
According to an internal EU document, seen by RTÉ News, the UK is seeking a range of grounds on which to refuse the extradition of British nationals.
The issue has held up a key part of the negotiations on the future EU-UK relationship.
The UK position has been set out in an internal EU document circulated to member states.
According to the document, London wants to secure mandatory exemptions on extraditing its nationals based on a number of principles.
However, the EU is strongly resisting the scope and range of UK demands.
The internal document says the demands are unacceptable, unprecedented and would be "one-sided".
Currently, EU member states are obliged to extradite their nationals if they are accused of committing crimes in other member states. The arrangements are enshrined in the European Arrest Warrant (EAW), to which all member states are signatories.
According to the House of Commons Library, extradition requests to the UK under the EAW increased from 1,865 in 2004 to 12,613 in 2015.
Requests made by the UK to other Member States went up from 96 to 228 per year over the same period.
Currently the EAW is the only means by which the PSNI can extradite a suspect to the Irish judicial authorities and vice versa.
According to the European Commission paper, the UK wants to retain the right to refuse the extradition of a UK subject to an EU member state on a number of grounds.
They include the individual's human rights, whether the alleged crime is "proportionate" to the extradition request, and whether or not the state requesting the extradition is ready to begin the trial.
In particular Britain wants to enjoy a mandatory right to refuse extradition if it is "contrary to the fundamental rights of a person according to the national law of the executing State [ie, the state which is extraditing the suspect]".
The EU note argues that such a ground for refusal is "very wide" and that it refers to "national" standards, and not "common" standards, such as those set out in the European Convention on Human Rights (ECHR).
European Commission negotiators believe such a ground for refusal to extradite is much broader than the EU's grounds, which are based on the principle of non-discrimination, as well as the guidance set by the ECHR.
They argue that such grounds are not found in other agreements between the EU and third countries, such as Norway and Iceland, nor are they part of the European Arrest Warrant.
The EU document states: "There is no need for such a ground for refusal in the agreement. As demonstrated by refusal would give a wide margin to refuse surrender (in particular since it refers to national law) and would thus be contrary to the objective of creating an effective surrender mechanism."
The paper says the UK also wants the right to refuse extradition if a British judge considers it "disproportionate".
According to the paper, this would depend on "the seriousness of the alleged conduct" and the likely penalty the suspect would face if he or she were found guilty.
EU negotiators again stress that such a ground for refusal is not in the agreements with Norway and Iceland, nor in the European Arrest Warrant.
They point out that the EU’s own draft legal text does not address the "proportionality" issue and argue that it should be the responsibility of the country issuing the arrest warrant to check its proportionality and not the country carrying out the extradition.
"There is no need for such a ground for refusal in the agreement," states the paper, "and it runs counter the objective to create an effective surrender mechanism, because it provides for a wide margin to refuse surrender."
The EU believes that under the European Arrest Warrant, problems associated with the "proportionality" of a warrant "seem to no longer exist".
London also wants to be able to refuse a suspect if the receiving justice system is not ready to proceed with a trial, according to the paper.
The paper says that this is if there are "reasonable grounds to believe that the issuing State has not made a decision to charge that person or has not made a decision to try that person, and the person's absence from the issuing State is not the sole reason for that failure".
Again, EU negotiators say this ground for refusal is not in other agreements, nor in the European Arrest Warrant.
The paper says this ground for refusing an extradition would "unduly limit the scope of surrender proceedings, based on a common law concept".
As such it would reduce the scope to extradite a suspect during the investigation of a crime.
"Such application during the investigation phase is of particular importance in cases where a requested person could re-offend or intimidate witnesses or victims," the paper states.
According to the paper Britain also wants to be able to issue a declaration that it is refusing the extradition of one of its nationals one the basis that it conflicts with the fundamental principles of UK national law, for example any found in the British constitution.
The paper says the European Commission believes that the UK’s additional grounds for refusing extradition of British nationals are "not acceptable".
"These grounds for refusal would be unprecedented. In our view, they would give too wide a margin of appreciation, or would excessively limit the scope of surrender proceedings, thus defeating the objective of creating an effective surrender mechanism," the paper concludes.
The Commission believes the rights of those being extradited are better safeguarded "by enshrining in the agreement the commitment to the ECHR and to allowing it to be invoked directly before national courts, as the EU has proposed".
The paper says that the UK’s proposals risk being used in a "one-sided" manner.
The Commission paper says it accepts the principle, proposed by the UK, that parties to the future relationship agreement must agree to either extradite the suspect or to try them in their own courts.
It is understood the UK believes the grounds for refusing extradition are important safeguards in any future arrangement with the EU and that they would also apply in the EU as well as the UK.
A complicating factor is that some member states have constitutional prohibitions on extraditing their citizens outside the EU.
London is thought to be seeking a commitment from the EU that in such cases the country refusing extradition will take over the prosecution of the suspect and will provide assistance to any UK witnesses or victims who may be involved.
It is understood a further offer from the UK would be that EU member states could surrender their nationals to the UK on the condition that they be returned home to serve their sentence, or where the person has been convicted to take over the sentence immediately.