Identity politics sidelines the common interest of those exploited and oppressed by capitalism.
It is a myth to believe that there ever existed in Britain or elsewhere a fully homogeneous working class. The class has always been divided by ethnicity, religion, geographical identity – and, of course, by sex.
The issue at stake, though, is whether you accentuate the diversity (the so-called identity politics) and then base your politics on building a would-be progressive coalition (women, blacks, Muslims, etc), or whether you emphasise the common interest of those exploited and oppressed by capitalism. I believe the latter to be correct.
Two overarching points resulting from Marxism are so obvious and well known to the intellectual left that they are apt to be forgotten! I shall restate them here: (1) capitalism – in the West at least - has led to such an expansion of the productive forces that it is possible for everyone to live free of poverty and economic anguish, but the capitalist system of ownership and income distribution prevents that, and (2) the fruits of wealth, deployed and enjoyed by capital, are the product of the exploitation of working people.
If ordinary people irrespective of ethnicity knew and internalised those points, then capitalism would be over by lunchtime on Tuesday.