If the UK never joined the EU/EEC in 1973 due to seeing a better economic fortune with the Commonwealth and US, or voted no in 1975, would they debating whether to join the EU today? Or would the issue be settled?
The EFTA might remain a bigger community too. If the EFTA is a power to be reckoned with in 1990/1 maybe Poland and the Baltic States join that instead of the EU?
Especially if the UK develops some degree of interaction with the common/single market...