When did the UK first open negotiations to join what became the European Union?

Question

In March 2016, the European Union agreed an arrangement with what country to reduce an increasingly overwhelming flow of migrants to EU countries?

Answer 1

1957
The UK started negotiating in 1957, applied to join in 1961, was vetoed by France, re-applied and was again vetoed by France in 1967, re-started talks in 1970 and finally joined in 1973. A national referendum in the UK in 1975 affirmed (67.2%) that it would stay in the EU, at the time the European Economic Community (EEC). A second national referendum in 2016 voted by a slim majority (51.89%) to leave, and the UK left in 2020.