Slight difference, the vote in 1975 was to join the EEC, the forerunner of the EU, which at that point was mainly a trade bloc. It wouldn't be a vote to leave, it would be a vote not to join in the first place.
British industry at that point seemed to be suffering from a lack of innovation, a lack of investment and a lack of quality, (see the Vauxhall Chevette, Austin Allegro and Ford Capri), of which the car industry was an example.
In essence, I think you'll see someone like Thatcher elected earlier and the devastation of under performing British industries far sooner and with far deeper cuts and the same with the unions.
I'd also expect Britain to move closer to the US politically and financially to the extent that there would be a fringe type party who would be seeking admittance into the United States. Think UKIP on stronger crack.
