Last Night's TV: Storyville &ndash; Amnesty! When They Are All Free, BBC4 <br/>Lead Balloon, BBC2

Virtue is its own reward, we're told, but it can dole out some ingenious punishments too, tormenting the well intentioned with unforeseen consequences. The Storyville film Amnesty! When They Are All Free began as what looked like a corporate celebration of the charity's 50th anniversary, full of fond memories and approving sentiments. But by the time it had finished it had become a lot more nuanced and ambiguous.

It was hardly a hatchet job, of course. To attack an institution this worthy would be to put yourself in singularly unpleasant company, alongside the torturers and despots and, as it happens, President Bush, who reacted indignantly to Amnesty's criticism of his administration. But it did acknowledge the tactical mistakes and the problems that success can bring. Intriguingly, it even had one of its more notable good causes – the Russian dissident Vladimir Bukovsky – taking President Bush's side, and rebuking Amnesty for describing Guantanamo as a "new gulag".

I suppose that might strike some as a little ungrateful, though Amnesty itself would have difficulty objecting, since one of its core principles is the defence of free opinion, however uncomfortable its expression might be. Founded by a London lawyer called Peter Benenson to take up the cause of prisoners of conscience it began as an article in The Observer, and as a triumph of optimism over realism. What real prospect was there, after all, that a hand-written letter from someone in Bolton would tweak the conscience of a dictator? But starting from the position that "if people do nothing, nothing will happen", activists and early members sat in pubs and badgered the powerful. And, remarkably, it did seem to have an effect. Even if the light turned on their activities was only one-candle power, regimes disliked it.

There were wobbles in the early days. Peter Benenson unwisely accepted funds from the British Government, damaging Amnesty's reputation for complete impartiality, and was fairly unceremoniously dumped by the organisation he had founded. And when the group started to campaign against torture it found that its adoption of a case could sometimes be counterproductive. Adopting Stalin's ruthless dictum – "no man, no problem" – the more murderous juntas simply made their dissidents disappear, forcing Amnesty to develop a 24-hour "we never close" policy, so that fresh arrests could be logged while there was still a person to worry about.

James Rogan's film also detailed the growing fame of the organisation, after fundraising events such as the Secret Policeman's Ball and the global Human Rights Now! rock tour had given it a certain cachet as the cause of the moment. The Secret Policemen's Ball, the voiceover noted somewhat innocently, "became a fixture amongst comedians wanting to give something back" (not to mention quite a few comedians who wanted to get something out of it). And when Amnesty's causes became voguish with Western politicians that caused problems too, making it easier for targeted regimes to dismiss them as a form of moral colonialism. Indeed – a little ironically given how it itself had leveraged publicity and exposure against oppression – the more visible the organisation got the more tricky things got for it.

Amnesty was judged to have got it wrong after it reacted too quickly, as it did following Iraq's invasion of Kuwait, when it helped spread a dubious story about babies being tossed out of incubators. And judged to have got it wrong when it didn't react fast enough, as happened during the Rwandan massacres, when its otherwise admirable policy of insisting on its own independent research meant it held fire while the whole world watched the genocide on television. It also has difficult decisions to make when an opposition to one infringement of human rights – such as Uganda's cruel homophobia – may threaten its ability to recruit members to protest against others. None of which even came close to eclipsing the charity's past successes and continuing work in providing eyewitnesses in some very dark corners of the world.

Rick Spleen is exactly the kind of comedian who would jockey for a good position at an Amnesty gig, the good cause foremost in his mind being the promotion of his own career. And then, of course, it would all go horribly wrong, since the essential dynamic of Lead Balloon, back for a fourth series, is that Rick should end up horribly humiliated by his own incontinent ambition. Or – as in last night's episode – by an incontinent pig, which anointed Rick with liquid manure while he was in the middle of trying to impress a Sunday Times journalist who'd turned up to write an "At Home With" feature.

Cruelly, the subject wasn't Rick at all but his long-suffering wife, Mel, who didn't really want to say yes in the first place but had been talked round by Rick. "It's probably not a bad time for me to put myself back in the public eye," he explained to his writing partner, Marty. "Any year now would be fine," replied Marty, whose drily unimpressed comments are an enjoyable grace note in the scripts. Planning to set-dress his life a little, Rick borrowed a Vietnamese pot-bellied pig. "I honestly think it's the kind of thing a couple like us would have," he told Mel. "It's not," she replied testily, "because otherwise we'd have one." The pig turned in a fine performance. As did everybody else, actually, in a comedy that has a lot of small supporting roles but no negligible ones.