The Home Secretary Theresa May has confirmed that the Coalition plans to use its veto to avoid implementing 130 new European Union legal measures relating to law and order.
The 'opt out' was negotiated by Ireland and the UK during negotiations on the Treaty of Lisbon and covers EU policies on asylum, visas and immigration, as well as the ability to opt-in or opt-out of any policies relating to justice or home affairs.
The opt-out effectively means that the UK has to choose to accept all 130 law and order measures agreed before the Treaty of Lisbon came into effect in 2009, or to opt-out of all of them.
Mrs May has indicated that the UK will decide to opt-out, on the basis that they can opt-in to certain provisions later on, with the agreement of other EU member states.
One of the crucial policies that the UK will not adopt is the controversial 'European Arrest Warrant' (EAW), which was backed by the Liberal Democrats during the last election. The EAW effectively obliges police in any member state to arrest, detain and transfer any citizen subject to the warrant, regardless of the country it emanates from.
The Tories oppose the EAW on the basis that it has led to unfair trials abroad for UK citizens, whilst the Lib Dems highlight its successes which include the repatriation of teacher Jeremy Forrest this month after he absconded with one of his students.
One of the crucial issues with the EAW is that UK courts have no power to examine the evidence against a Briton accused of a crime abroad, and instead must simply rubber-stamp their extradition. The result is that British citizens can face trials in EU countries where the court systems are less robust and fair, and may then face lengthy jail sentences as a result.
In a statement the Liberal Democrats maintained their support for the EAW.
"The value of EU police co-operation has been demonstrated only today with the arrest using the European arrest warrant of Jeremy Forrest," the statement read.
"Any opt out in this area is still under review and discussion. Our decision must follow the interests of national security, public safety and Britain's international reputation for leadership on cross-border security matters," it concluded.
EU law opt-out plan to be announced (BBC News)