A former police chief has accused the UK Government of making it "virtually impossible" to catch Scottish gangsters hiding on the continent.

Labour MSP Graeme Pearson, a former head of the Scottish Crime and Drug Enforcement Agency, has added his voice to serving officers concerned about a Conservative threat to ditch European Arrest Warrants (EAWs). SCDEA worked with colleagues in countries like Spain and the Netherlands to build a case against criminals such as cocaine kingpin Jamie "The Iceman" Stephenson.

Home Secretary Theresa May has signalled the UK will pull out of more than 100 European Union-wide police and justice agreements cemented in the Lisbon Treaty of 2009, including EAWs.

Mr Pearson said: "Organised criminals cross the borders of nation states. The absence of European Arrest Warrants will make tracking down such figures – and people like prolific sex offenders – virtually impossible."

Yesterday The Herald revealed senior serving officers in Scotland were concerned about the moves, which have been prompted by eurosceptics within Ms May's party.

Justice Secretary Kenny MacAskill has said the proposed opt-out is "jeopardising the administration of justice in Scotland".

Conservatives argue that foreign police forces are issuing EAWs for trivial matters and that British nationals are at risk of long periods on remand in European justice systems.

Scottish Conservative chief whip John Lamont said: "The UK Government is acting in the best interests of British citizens by opting out of the EAW, which we should not forget allows other European nations to demand British citizens are arrested and transferred for trial abroad. All political parties at Westminster have agreed that the warrant needs reformed.

"It has famously been used recently to extradite a Polish national accused of stealing a wheelbarrow with a value of £30. The proceedings for extradition from this country cost £30,000."

Nationalist MSP Colin Keir accused Conservatives of being "prepared to assist criminals in fleeing from justice merely in order to appease their own backbenchers".

Liberal Democrats are understood to be lobbying for the UK to keep the warrants.