 Complete the following phrase:  The 2015-16 United Kingdom renegotiation of European Union membership was an unimplemented non-binding package of changes to the United Kingdoms terms of its European Union EU membership and changes to EU rules which was first proposed by Prime Minister David Cameron in January 2013, with negotiations beginning in the summer of 2015 following the outcome of the UK General Election. The package was agreed by the President of the European Council Donald Tusk, and approved by EU leaders of all 27 other countries at the European Council session in Brussels on 1819 February 2016 between the United Kingdom and the rest of the European Union. The changes were intended to take effect following a vote for Remain in the UKs 