Dozens of Scotland's most wanted criminals were fast-tracked back from Europe to face prosecution before Brexit.
Police Scotland feared losing the right to use the European Arrest Warrant (EAW) as the UK left the EU on Thursday.
So a team of specialist officers spent 2020 targeting a list of fugitives hiding out across the continent and have reduced the number outstanding from a peak of around 70 to single figures.
A senior Police Scotland source said: "The Fugitive Unit worked flat out to try to minimise the consequences of Brexit.
"When the pandemic took hold, it really was a double whammy for the force.
"It's amazing the unit has been able to secure the return of so many suspects from so many different countries, especially with all the additional problems the pandemic threw up."
Specialist officers in the Fugitive Active Search Team (FAST) were driven to the remarkable results by the need to speed up operations throughout 2020 as fears that security talks between UK forces and their former European allies would collapse after Brexit.
As a result of the Brexit deal agreed on Christmas Eve, the UK will no longer have access to the EAW, which streamlines extradition processes for EU member states.
But senior police figures were relieved that some agreement was made as a no-deal Brexit would have been likely to cause even greater problems with co-operation reduced to a minimum.
In October, with a deal on future security links at that time more advanced than the trade deal, a major crack in any future links appeared.
Some EU nations, including Germany and Poland, said they would not agree to extradite their citizens back to the UK even to face a murder charge if there was no deal, as they feared the UK would not guarantee their human rights.
The EAW system was introduced in 2002 and adopted by the UK in 2004 to streamline the transfer of wanted fugitives between EU nations.
From January 1, UK forces now have to revert to Interpol Red Notices supported by the 1957 Extradition Act, a more lengthy and complex process.
A senior source explained: "As long as we retain a reciprocal arrangement with the EU, which is far more likely now with a deal, we can still ask them to arrest and hold suspects for us and we will do the same for them.
"Extradition will become more complex on both sides but suspects will be detained in custody, so that's not a disaster."
The insider said the other major hit UK police forces would take was loss of access to the Schengen Information System, which would see them revert back to the Interpol database.
The severity of the loss is underlined by the fact that UK forces searched the Schengen SISII system more than 600million times last year.
The system holds some 80million pieces of information on criminals, terrorists and missing persons.
The Interpol database holds only hundreds of thousands of pieces of information.
The source added: "No one should pretend that won't be a huge loss."
The new arrangements will tie up more Government resources and are likely to leave criminals either at large or remanded abroad to await extradition, leaving victims waiting longer for justice.
One informed source added: "The EAW system is one that Police Scotland's officers have been working with for nearly 20 years – long before it was a single force.
"It is about as smooth a system as you can get for a process as complicated as extraditing someone accused of a crime in another country to that nation.
"Both sides involved are now going to have to start using rules and regulations they have never used before, while some existing rules will still apply in certain areas – it's going to be a nightmare."
Police Scotland confirmed they had made plans for leaving the EU.
Assistant Chief Constable for Organised Crime, Counter Terrorism and Intelligence, Pat Campbell, said: "We have been planning and preparing for Britain's exit from the European Union for some time now.
"We have increased the size of our International Unit to enable us to continue to share intelligence and interact with member states in a timely manner.
"We have also increased our Border Policing command, who provide a presence and reassurance at ports and airports.
"We maintain close working relationships established over many years with a wide range of partners including Europol, Interpol and the National Crime Agency."
