Both are far-left wing authoritarian organisations, committed to central State command and control, restriction of free markets and both are profoundly illiberal.
So when the Guardian's diary editor Hugh Muir writes in this morning's paper that;
Look at constituency parties up and down the country and it is clear that the party has hollowed out. The unions and many of the sorts on the left despised by New Labour provided the link for the party to operate in many poorer, inner-city communities. New Labour cut the cord and in so doing left those communities to drift.To drift - and to join the BNP in record numbers, as New Labour were deaf to the voices of 'the sorts of the left'.
Muir is right. The unreconstructed old-left still lives, and can barely restrain itself from uttering when meeting Ms Harman "Cup of tea please Luv, two sugars". No doubt in darkest Lancashire the phrase 'Nig Nogs' still lives alongside 'Comrade' and 'Brother'. The Unions and the BNP are natural bedfellows. Why split Labour's core vote?