Arguing that, building on these concessions the Maastricht and subsequent treaties, transcended the Single Market vision and committed Britain to an evolving "federal Europe", in 2015 Conservative "Euro-sceptics" secured a referendum on continued UK treaty accession. While presuming that Britain would remain "part" of a "European free trade zone from Iceland to the Russian border", the official Vote Leave campaign and its allies proved victorious in the "Brexit" referendum of June 2016. After rejecting calls to negotiate continued membership of the Single Market or a free-trade agreement based on regulatory alignment with the Single Market, under the terms of the October 2019 Withdrawal Agreement the Conservative government of Boris Johnson, withdrew the United Kingdom from the European Union, and thus from the SEA, at the end of January 2020.