Even in the 1970s the Labour party was still attuned to its white working-class base, even if there were Marxist types pushing hard-left stuff in the party itself. They opposed globalism and were actually against joining the EEC (the precursor to the modern EU). They were not openly pro-immigration.

The landscape changed after 1979 when Maggie Thatcher's Tories won the election. That was a rejection of both Old Labour and the Old Right like Enoch Powell. Thatcher fully embraced "colourblind" neoliberalism, and even though net immigration was actually at a negative during her years in office, they laid the groundwork for Zionist neocon/neolib New Labour and mass immigration. Thatcher herself once said her greatest achievement was Tony Blair and New Labour. Blair's economic advisors were Thatcherites, I remember one of them (a contemptible scumbag) was interviewed and more or less said "tough shit, it has to be done for the good of the economy, just like closing the mines" when questioned on the public's opposition to mass immigration.

"International socialism" was never an option, we got international capitalism.