One of the positives of the Scottish independence debate has been how it has forced all sides to return to first principles and examine the foundations of their ideologies. This most obviously involves the difference between socialism and nationalism. For followers of the former, solidarities of class trump those of nationhood. A worker in Dundee has more in common with a worker in Durham than he or she does with a businessman in Dunfermline. Any attempt to divide workers along alternative lines only serves to reinforce the dominant economic system.

It is this point that Ed Miliband will make with admirable clarity in his speech tomorrow at the TUC general council dinner in Liverpool.

He will say: "The Labour movement was founded on the principle of solidarity. You know that unity is strength. You know that we achieve more together than we can do alone. You know that what working people have in common matters more than any division of creed, race or region. Or even nation.

"And that is why trade unions, trade unionists and the Labour movement are playing such an important role in keeping Scotland and the United Kingdom together.

"From USDAW to the NUM, from the GMB to ASLEF, from Community to the CWU, trade unions are fighting for the right kind of change in Scotland - and the whole of the United Kingdom."

With Labour voters the key swing group in the referendum (35 per cent now support independence, according to the latest YouGov poll, up from just 18 per cent a month ago), the message that UK workers should unite along class lines, not divide along national ones, is one that must be delivered repeatedly. But after seven years of SNP government, and the cynicism induced by New Labour, the danger for socialists is that this argument has lost much of the potency it once held.