Hunt is a subtle enough biographer to let Engels flourish in his contradictions - not least of which was that he earned his (and Marx's) keep for more than 20 years as an agent of that industrial capitalism whose ruthless logic he dedicated his life to exposing. The scale of Marx's economic dependence on Engels was truly astonishing. "Can you manage with £350 [almost £35,000 in today's money] for your usual regular needs for a year?" Engels inquired of his friend in 1869 when he was trying to extricate himself from his Manchester business commitments. In addition to the "usual regular needs", there were endless petitions for cash, as the profligate Marxes moved on to ever more spacious and expensive lodgings, pursued by bailiffs and angry tradesmen. As if that were not enough, Engels also bankrolled a motley band of hangers-on, including Marx's wastrel son-in-law, Paul Lafargue, a no-hoper who achieved a modest notoriety as the author of the idler tract, The Right to be Lazy.

Engels's friendship with Mary Burns, the semi-literate Manchester Irish woman who was his companion and lover for 20 years until her death in 1863, is beautifully handled, as is his subsequent cohabitation with Mary's entirely illiterate younger sister, Lizzy. But the relationship with Marx rightly occupies centre stage. This was a true marriage of opposites. Engels was tall, thin, had beautiful smooth skin and was attractive to women. Marx was squat and covered in carbuncles. Whereas Engels was sweet-natured, equable and of sunny disposition, Marx was impetuous, self-absorbed and tortured. Yet the two had no difficulty in joining forces, especially when an opponent or competitor hove into sight. The "tedious bludgeoning", as Hunt calls it, of ideological foes was one of the things that kept them afloat as a team.

In what sense should we hold Engels responsible for the crimes and oppression of the totalitarian regimes erected in his name? Hunt is quite unequivocal on this point. Engels was no "Leninist". He was sceptical of Russia's chances of mounting a successful revolution and he never espoused the idea of a "vanguard party". He preferred to set his hopes on the gradually deepening contradictions within western capitalism - in this sense he has much more in common with the Mensheviks than with the authors of the October Revolution. He was not a dogmatist, but a man who was forever changing his mind and looking for new answers. The stony-browed, authoritarian Engels of Soviet statuary now seems as bygone as ancient Egypt. By contrast, the genial, interesting and learned Victorian who inhabits Hunt's pages is a thoughtful contemporary who speaks eloquently of our current predicaments. That is just one of the paradoxical pleasures of this delightful book.