Twenty European Union states are refusing to guarantee that suspected criminals who are citizens of their country can be extradited to the UK.
Ten EU countries have declined point blank to allow such extraditions, two will do so only if the suspected criminal agrees and eight have attached other restrictions.
The development emerged in recently released documents from Brussels and reflects the fact that Brexit means the UK is no longer part of the European Arrest Warrant.
The current setup potentially undercuts the ability for Europeans who are suspected of committing crimes in the UK to be returned to face justice after fleeing to the Continent.
Lawyers have warned it could also artificially keep prison populations high as judges may be reluctant to grant bail over fears of European suspects leaving the country and not returning.
The position of each of the 27 EU member states towards extradition and the UK was contaminated in an EU notification note issued on April 6.
Under the European Arrest Warrant suspected criminals could be extradited easily within the bloc.
But with Britain now out of the EU, individual member states can decide their position. Ten EU states have said they will not hand over citizens suspected of crimes to the UK: Germany, Greece, France, Croatia, Latvia, Poland, Slovenia, Slovakia, Finland, Sweden.
A further two, Czech Republic and Austria, will do so only if the suspect agrees. Eight more countries attach restrictions, such as prison sentences being served in home nations.
Only the remaining seven EU member states broadly agree to reciprocity with the UK: Belgium, Ireland, Spain, Italy, Bulgaria, Cyprus and Malta.
It means that an imbalance exists given the UK’s willingness to extradite Britons suspected of committing crimes in EU countries.
Edward Grange, a partner at Corker Binning solicitors, said: “The UK will continue to extradite its own nationals as it has given no notification that the nationality bar will apply.
“Indeed, this stance continues the UK’s long standing approach that an individual’s nationality alone should not prevent extradition.”
A Home Office spokesman said: “The UK agreed a comprehensive security agreement with the EU, which includes streamlined extradition arrangements.
“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.
“It is the UK’s longstanding policy not to distinguish between UK nationals and others in extradition proceedings in order to ensure individuals can be brought to justice.”
In a separate development, the European Commission has told EU member states it opposed the UK’s application to join the Lugano Convention.
The convention is a treaty that decides which court has jurisdiction in cross border civil and commercial disputes and ensures judgements are enforced across borders.