"Could you really envisage putting that question?" said a Red Cross veteran sceptically, after John Simpson suggested that he might have asked SS officers what was happening in the shower rooms of German concentration camps. The veteran's tone was one of incredulity at the naivety of the remark but he couldn't know that Simpson has reasonable grounds for replying "Yes".

Last week, in the first of this intriguing series about the Red Cross, Crossing the Lines (BBC2) he met a heavily-armed Colombian guerrilla who initially claimed to observe the Geneva convention. "But surely you recognise that kidnapping people is in direct contravention of the Geneva convention," Simpson replied calmly. There was a pause, and then with a winning grin the guerrilla admitted the inconsistency of his position. Regrettably, he explained, "since no-one finances our socialist projects we get the capitalists to help us". They don't always want to, but a few months in the mountains often changes their minds.

That first programme was a sympathetic consideration of the difficulties faced by the organisation - in particular in maintaining its basic principle of neutrality, which means that it will utter no public denunciations about the atrocities and conditions it encounters. From the inside this is seen as a necessary condition of the Red Cross's work - which is to get help to anyone who needs it. From the outside it can generate some odd paradoxes - Simpson also accompanied a Colombian delegate inside one of the country's horrendous jails, to find that she could secure artificial limbs for a man who had blown his arm and leg off while attacking civilians, but could not repair the shattered toilets in the jail's top-security wing, because that would be seen as intruding on the government's responsibilities. This week's programme showed how the attempt to stay on the ethical tightrope strung up by such fastidious distinctions might itself be seen as a kind of atrocity.

"Betrayal" began with talk about a "dark secret at the heart of the world's oldest humanitarian organisation", and amplified the sense of revelation with some affectedly underlit film of Simpson flicking through wartime documents. The truth was that it was an open secret - he was only in the Red Cross archives because they had switched the light on in the first place, their new openness being part of a recognition that its record on the extermination of the Jews is not a proud one. Over fifty years ago, the same arguments about impartiality led to a silence about the camps which amounted to suppression of evidence, a self-imposed gag which was pulled even tighter by senior figures' sympathies for the German state as well as a fear that the organisation's work with prisoners of war might be jeopardised.

Even after the crushing I-told-you-so of the Holocaust, this debate tingles with a residual electricity. Simpson's summation was scrupulously fair, but it still begged the question of how effective any protest could have been - the Nazis not being noted for their openness to debate this matter. The doubt remained, although if the Red Cross had spoken out, might other circumspect witnesses - the Pope and the Allies among them - have been forced to do more?

Presumably the eco-warriors buried beneath the site of Manchester's second runway think of themselves as witnesses to the truth. Last night's episode of Made in Manchester (BBC2) offered evidence that they were having some kind of effect - even if this particular patch of paradise will shortly be skid-marked tarmac. The airport has a full time ecologist, who cheerfully busies himself picking up minute water-snails to save them from destruction. The most ludicrous of his activities consisted of carefully peeling up patches of non-descript meadow and then piecing them together somewhere else.

In the world of pain routinely inhabited by the Red Cross, this exercise had an almost Swiftian futility about it, but I suppose it must keep someone happy.