When Sadiq Khan accused David Cameron, in his “multiculturalism” speech in Berlin, of “writing propaganda for the English Defence League”, he did not get a lot of support from his own side.

None of his senior colleagues condemned him. But they were quick to be muted.

He did get backing from some quarters. Atul Hatwal, in Uncut, for instance, was unusually unstinting in his praise:

“While others were either hiding behind the sofa or couching their disapproval in the gentlest and most respectful of terms, only Khan called it as it was.

The Labour party lost its compass on this issue years ago. Under Blair and Brown the traffic was only ever one way. For years the right have been able to ritually burn multicultural straw men with impunity. The mark of Duffy has only made the party more timid.

But sometimes there are issues where it is simply a matter of right and wrong. No politics, no triangulation and no trading. These irreducible beliefs used to be what distinguished Labour and gave the party its moral centre”.

Khan’s shadow cabinet colleagues remained ominously, but tactfully, silent. The Labour default setting on race held firm: say nothing if you can help it.

Elsewhere on the front bench, though, some shadow ministerial colleagues were rather more boisterous in their pronouncements.

Step forward Ian Austin, shadow sports minister and MP for Dudley North, in which marginal seat the BNP looms large. Hewn from the illiberal granite of West Midlands Labour, Austin was clearly incensed at Khan’s intervention and not prepared to join former Brownite colleagues like Douglas Alexander and Yvette Cooper in taking it lying down.

At business questions that week, he told the House of Commons:

“May I add my voice to a call for a debate on the prime minister’s important speech at the weekend, so that we can discuss in the House how we can build a much stronger sense of what it means to be British, based on the contribution that people are prepared to make, whether they want to work hard, play by the rules, pay their way, whether they are prepared to speak English, because that is the only way to play a full role in British society, and their commitment to the great British values of democracy, equality, freedom, fairness and tolerance”?

“The prime minister’s important speech”. Not exactly “propaganda for the EDL”. Austin’s message is pretty plain. On this issue, for him, Cameron is on the side of the angels, Khan on the side of the others.

Speaking to the Express and Star, Austin warmed to his theme:

“Ever since I became an MP I have been campaigning to build a much stronger sense of what it means to be British. It is only by building a stronger sense of patriotism and national pride, that we can tackle extremism and build a stronger and more united society. If we don’t stand up and say Britain’s history and its values make this the greatest country in the world, how on earth can we expect anyone else to believe it? And if people do not learn to speak English how can they play a full role in society”?

Khan and Austin represent opposite extremes of a major divide within Labour. Neither is alone. While the likes of Atul Hatwal are trenchant in support of Khan, Britain’s longest serving Muslim MP, Khalid Mahmood, spent most of the day of Cameron’s speech telling any broadcaster who would listen that the PM’s central argument was right.

These divisions matter because opinions are very strongly held on either side. And because it is an issue which, directly, shifts votes.

It is surprising, in which case, that these splits are not receiving more attention.