Judge Ian Forrester, who sits as a member of the general court of the European Court of Justice in Luxembourg, said police forces in the UK would face a “gap” in their capabilities if they were no longer able to co-operate with European counterparts on the same basis as now.
While London and Brussels have said they are committed to working closely on policing and security after Brexit, uncertainty surrounds UK participation in Europol – the European policing agency – and use of the EAW, which allows speedy extradition of suspects within the EU.
A total of 1,101 suspects were apprehended and 956 were extradited to Britain from the EU through the EAW from 2010 to 2016.
However, the UK is expected to leave the agreement as several EU member states have a constitutional ban against extradition outside the bloc.
Mr Forrester said on Europol: “When you are talking criminal enforcement, criminal investigation, there needs to be a legal framework.
“It can’t be done on the basis of friendly, cordial understanding.
“If those mechanisms were to cease to apply in the United Kingdom, then something new has to take their place ... one would assume there’s a gap.”