THERE is blood on the streets of London and Paris — and it’s Jewish blood. Two costume dramas about anti-Semitic violence began last week, making an instructive contrast. In Ridley Road (BBC1, Sundays), set in 1962 and “inspired by true events”, gorgeous Vivien Epstein runs off to London to escape from her stifling Orthodox Jewish parents and her arranged marriage.

Caught up by chance in Colin Jordan’s National Socialist Movement’s Trafalgar Square rally, she is appalled to recognise her equally Jewish boyfriend supporting the leader on the platform, yelling vile slogans, and enthusiastically joining the ensuing mêlée. Bit by bit, she realises that he is, in fact, an undercover agent, passing on the fascists’ plans to the vigilante squad led by her Uncle Soly, the black sheep of the family. She joins the cause, and similarly infiltrates Jordan’s secret training camp.

This is Britain’s 1960s watershed: pop culture is taking over, post-war certainties are collapsing, terraced houses are being torn down, and the working class rehoused in tower blocks; immigration is causing suspicion and backlash.

All this is admirable in concept; but it doesn’t really work. The plot is paper-thin, and the pile-up of improbabilities is too great. This is a lost opportunity: the theme deserves a far more rigorous head as well as heart.

Paris Police 1900 (BBC4, Saturdays) is, oddly, far more serious, and also far less. Here, on the eve of Dreyfus’s retrial for treason, anti-Semitism is supported by respected leading figures. It might even take over the government, as Jordan never seriously could. We follow an honourable police officer combating the corruption engulfing his profession and society generally.

It is far more sexual, and far, far more explicitly violent. But, somehow, the wholehearted verve with which the cast throws itself into the enormity that they present conveys more effectively the vital anti-hatred message; by contrast, Ridley Road, which takes itself so seriously, seems solemn and worthy and therefore less compelling.

Guardians of public morals must be seriously worried about Sir David Attenborough’s growing obsession with sex. His latest BBC1 series The Mating Game (BBC1, Sundays) is concerned with nothing else — a telling commentary on current public mores, broadcast as it is in what used to be the alternative-to-evensong slot. This last one focused on how they do it underwater, from humpbacked whales to seahorses.

The clown fish must pose terrible problems to Christians determined to uphold fundamentalist sexual definitions. Whenever a group’s dominant female leaves, the male next in line promptly changes sex to take her place. What was God thinking of? Fishy congress usually involves a preceding bout of rivalrous male violence, but the actual coupling is serene and beautiful.