PERHAPS the single most ugly page in post-war industrial relations history is the story of how some sections of the working class reacted to Enoch Powell’s ‘rivers of blood’ speech in 1968.

London dockers, Smithfield meat porters, builders and workforces at several small factories warmly responded to the Tory MP’s deliberate attempt to incite racial hatred against black people in this country, showing their enthusiasm with a wave of unofficial stoppages.

Comparisons have been drawn by some parts of the left between this episode and the events of the last few days, which have seen a dispute against the use of foreign labour at Lindsey oil refinery spark a wave of wildcat strikes across the construction industry.

I’ve been trying to think the issue through this morning, and have concluded that the cases are simply not analogous. Let me give some of the reasons.

First, the Powell walkouts were an expression of political support for the incendiary rhetoric this man directed against the Race Relations Bill, including his argument that Britons were becoming ‘strangers in their own country’, and his prediction of widespread bloodshed unless the government turned to voluntary repatriation.

The underlying issue in the current wildcats is a genuine industrial grievance. The reality is that tensions have been building in British workplaces over the last quarter of a century of management triumphalism. Things always were going to blow at some point; the issue that provides the detonator is thus completely incidental.

Second, there is the scale and geographical spread of the stoppages. The Powell strikes were overwhelmingly based in East London and involved relatively small layers. Various books in my library give different figures for how many dockers joined in, but the estimates range from a low of 200 to a high of 1,000. The Smithfield participants were just a few dozen. By contrast, the 2009 strikewave extends nationwide, and has already won the backing of greater numbers.

Third, while the principal slogan – ‘British jobs for British workers’ – is clearly misguided, wrong-headed and of infelicitous provenance, today’s context is thankfully very different to the one in which the National Front launched the catchphrase in the 1970s. The category of ‘British workers’ now firmly includes British workers of black or Asian origin. That makes it qualitatively different from ‘Don’t knock Enoch’ or ‘Back Britain, not black Britain’.

This is not to say that it is a demand the left would have chosen, or even that its overtly nationalist implications are not divisive. Of course it represents a propaganda godsend for the British National Party. And yes – to borrow the phrase Greg Dyke used in relation to the BBC – the photographs of the picket line look hideously white.

But the call does not seem to me to be consciously racist in motivation. As the old joke goes, I wouldn’t start from here. But to use that as an excuse for indifference or inaction would be a tactical error.

Oh, and here’s one further thing to bear in mind; just nine years after London dockers marched in praise of Powell, they were marching in solidarity with low-paid Asian women at the Grunwick film processing plant.

But it is up to the left to ensure that the new militancy draws the right political conclusions. What is more, we should be fully aware of what will happen if we fail.