The Law Society says plans to opt-out of EU police and crime cooperation measures may jeopardise the UK’s ability to fight cross border crime.
Home Secretary Theresa May has said she is minded to exercise the UK’s option on 133 European crime-fighting and justice measures, including the European Arrest Warrant.
She has until 2014 to opt-out.
Police chiefs have warned that the move could “isolate” the UK.
The opt-out would mean all European judicial co-operation measures would cease to apply to the UK after 2014.
Chair of the Law Society’s Criminal Law Committee, Richard Atkinson, will give evidence about the opt-out to a House of Lords EU Sub-Committee later today.
He told Central Lobby: “The European Arrest Warrant is an improvement on previous measures, which posed more problems, and it would be detrimental to take a step backwards, as it could leave suspects being held in pre-trial detention for longer periods.
“Systems need to be in place to facilitate effective cross-border co-operation in criminal justice matters between Member States and provide for corresponding procedural rights for victims and suspects.
“The UK will remain bound by the EU criminal justice measures agreed after the Lisbon Treaty even if it exercises the opt-out.
“We can see no reason for opting out of measures which on anyone's analysis are not harmful and a good number of which are beneficial and which we will need to opt back into at potentially great cost to the taxpayers of this country.”
Mr Atkinson also questioned the implications for its involvement with Eurojust, the European Union body established to stimulate and improve the co-ordination of investigations and prosecutions among the competent judicial authorities of the European Union Member States when they deal with serious cross-border and organised crime.
“Should the UK fail to opt in to new measures likely to be proposed for these agencies, the UK may essentially fall out of those existing measures.”
Scottish police chiefs have raised concerns about the opt-out in a submission to the Lords committee.
"Scottish officers will encounter complex and protracted processes when dealing with offenders effectively both within the Scottish and European criminal justice process and partner agencies,” the Association of Chief Police Officers in Scotland said.
“This could effectively isolate the UK in respect of serious and organised cross-border crime, thus providing a refuge for foreign criminals within our borders."