As in, what led to the UK not joining in 1967 but joining in 73? What was the national mood around this in the first place? What were people expecting the advantages to be? What sort of questions were debated around the referendum of 1975? Were there national splits between the four nations like we've seen this week?
The reason for the UK not joining the EEC in '67 was because Charles De Gaulle yet again (like in 1963) vetoed our entry you can read more about De Gaulle's veto on this recent askhistorians thread
That's all I'm really comfortable saying as this isn't my area so without I'd have to pass the baton over to /u/Copperbrook or /u/agentdcf. I hope this helped a little :)