This report is the Home Affairs Committee's response to the House's invitation of 15 July 2013, together with the Justice and European Scrutiny Committees, to submit a report by the end of October 2013 relevant to the exercise of the block opt-out of pre-Lisbon Treaty EU police and criminal justice measures, before the start of negotiations between the Government and the European Commission, Council and other EU member states on measures which the UK wishes to rejoin following exercise of the block opt-out. The Government has given notification of its intention to exercise the block opt-out. Its right to do so, and the conditions attached to the exercise of that right, are contained in Article 10 of Protocol 36 annexed to the EU Treaties. The block opt-out covers 130 EU police and criminal justice measures which had been adopted prior to 1 December 2009, the date of the entry into force of the Lisbon Treaty. The Committee has also set out: (i) That there are many problems with the European Arrest Warrant, in its existing form, in particular that it is on a system of mutual recognition of legal systems which in reality vary significantly; (ii) The Committee welcomes and supports the Government's reform package for the arrest warrant; (iii) The Committee recommends separate votes on the arrest warrant to the rest of the opt-in package at an early stage to provide a parliamentary mandate for the Government's negotiations.; (iv) The Committee concludes that if the Government proceeds with the opt-in as proposed, it will not result in any repatriation of powers. Indeed, the increased jurisdiction of the European Court of Justice may result in a net flow of powers in the opposite direction.