The only comment I can make to your statement is at least the old Labour Party (and I am not fan of them) was anti EC as I grew Conservatives were pro Europe and Labour was anti.
Is that how you rememeber it Ivan?
My recollection is that both Labour and the Tories have both pro and anti EU people. In Labour, you have Tony Blair who is pro-EU, but you also have people like Dennis Skinner (aka, the Beast of Bolsover) who is totally against the EU. Amongst the Tories, there's people like Sir Michael Spicer who wrote a powerful anti-EU book, and Kenneth Clarke who claims to be in favour of further European integration.
Both parties, in my opinion, have been riven with divisions on this one subject for a very long time. Labour in the past decade has overall, had more of the pro-EU persuasion, and the Tories, more of the anti-EU persuasion.
Best Regards, Ivan