Membership gives British citizens the right to live and work anywhere in the EU — unlike citizens of other countries, who must seek complicated and often hard-to-get residency and work permits.
Mark Gray, a spokesman for the EU, said the bloc affects almost all aspects of the lives of Britons, from the quality of the water they swim in at beaches or in pools, to the quality of the orange juice they have for breakfast and the conditions in the offices where they work.
But many Britons — like citizens elsewhere in the EU — see the union as a faceless beast imposing rules and spending on needless things and threatening sovereignty.
Britain's relations with Europe have been strained since the end of World War II. It did not join the European Steel and Coal Community, the forebear of what would later become the European Union, in 1951.
Britain later realized there were benefits accruing from joining up with some of its wartime friends and foes, and joined the evolving European bloc in the 1970s. It has stood against many efforts to forge closer ties, notably the creation of the euro, but was at the forefront of the drive to create a single market.
Don Melvin in Brussels and Martin Benedyk in Davos, Switzerland, contributed to this report.
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