Norway and Iceland signed a treaty with the EU in 2009 to apply certain provisions of the Decisions. Norway ratified the agreement and it entered into force for it as of 1 December 2020, while Iceland has not ratified as of October 2020. Denmark, Ireland and the United Kingdom have opt-outs from participating in the Council Decision approving the agreement with Norway and Iceland. While Ireland and the United Kingdom decided to opt-in, the agreement does not apply to Denmark. The Council of the European Union authorized the launch of negotiations with Switzerland and Liechtenstein on their participation in the Prüm regime in June 2016. Proposals to conclude agreements with each state were put forward by the European Commission in January 2019. Ireland and the UK again opted to participate in the agreement. The agreements were signed on 27 June 2019. On the 23 June 2016 the United Kingdom voted to leave the EU. After withdrawal negotiations concluded, the United Kingdom left the EU on the 31 January 2020.