Not true. We were never hoodwinked. We actually left a free trade zone, EFTA, to join the EEC (the old name for the EU), specifically because we felt free trade was not enough.
The Wilson government, setting out its reasons for applying in 1967, stressed that “Europe is now faced with the opportunity of a great move forward in political unity and we can — and indeed we must — play our full part in it”. Evidence
And before the referendum in 1975, national newspapers on both left and right were clear that a degree of political, not just economic, integration was proposed. More details