Is an archaic law being used to clear 'working class scum' off the streets?

That's the idea behind Common, a new drama from Jimmy McGovern. The law in question is known as 'joint enterprise', a legal principle which assigns collective guilt to a group even if only one of them committed the crime. It's sufficient simply to be present at the scene and to be judged to be egging someone on or even just giving them a knowing wink. All parties to the crime will be judged equally guilty.

The law was introduced in the old days to stop aristocrats from duelling, but McGovern suggests it has been revived of late to target the working class. All those gangs of feral youths on our streets can now be mopped up, en masse, if just one of them commits a crime.

JohnJo drives some local hard nuts to the pizza place, quietly glad that the big tough guys want to hang about with him. He stops the car and, as the others rush into the shop, he calls after them 'no mushrooms on mine!' Johnjo is a nice, gullible boy, unaware the gang just needed transport to the cafe where they could confront an enemy. As he sits in the car, still hoping he won't get mushrooms, a murder takes place. The gang pile into the car, screaming at him to drive. Johnjo is now, under the principle of joint enterprise, guilty of murder.

He is clearly innocent, as are the other lads involved. The knife was wielded by just one - a pudgy, repellent creature called Kieran Gillespie who threatens Johnjo, saying he must keep quiet because the worst thing, in this working class neighbourhood, is to be a grass. 'If you grass you're dead. And your mum's dead and your dad's dead and your house is torched,' he says.

Even though Jimmy McGovern is known for championing the working class, he doesn't shy away from showing the 'feral' side of life on this estate. There's no salt-of-the-earth solidarity here. Instead, you'll get 'torched' if you grass on the Gillespies whereas the bereaved family will 'torch' you if you don't.

But this wasn't to be a chilling, realistic drama as the character of Johnjo was all candy floss. He was just too soft and gentle and this was a mistake as we're supposed to rail against the injustice he faces. But instead of inspiring anger and upset, you just want to pat his head and get him a nice hot water bottle. He was so dainty - even suffering from haemophilia, saying literally and figuratively, that the slightest jolt to this poor lad will hurt him. See how innocent he is! The feeling was that McGovern was preaching to us, but using a screeching megaphone instead of subtle, realistic characters.

The dialogue was also rather flat, with clunking lines such as 'he's only gone and stabbed him!' I can't think of one fragment which sent a shaft of horror straight to the heart or which finely and precisely nailed a scene, as the best dialogue should. However, the acting was brilliant, especially from Samantha Oliver, the grieving mother. The scene where she views her son's body was hard to watch. She starts to scream, but it isn't a cliched screen wail: she pounds the glass wall and goes on and on doing it until you want to look away.

Nonetheless, this remains a worthy programme for the issues it raised: how the black cloak of joint enterprise can be thrown over you and bundle you into a life sentence when you were just going out for pizza. Also, for the fact that Johnjo willingly told the police his story, whereas the one who was unco-operative was able to trade his statement for immunity - the lesson being that honesty doesn't pay. There was also a sad subplot about the grieving mother's inability to find the £5k needed for the funeral and the special white coffin she wanted. She applies for bank loans and is dismissed each time whilst the funeral director insists that he wants the money up front (though would such a careful professional, when the mother has minutes before been wailing, say such a thing or is this just McGovern and his megaphone again? The working classes can't afford nice coffins! Should only the toffs be buried in white!)

So, the programme was packed with lessons to be learned but those lessons would have been better conveyed if Jimmy McGovern had put the megaphone down and let the story tell itself. The juxtaposition of good Johnjo versus feral Kieran was too convenient and so lacked the steel of realism, and what's the point of kitchen-sink dramas if they're lacking realism? JohnJo would still have been innocent if he'd had a pit bull and a string of previous convictions. Had he been a 'bad boy' then we'd have seen him battling prejudice and middle-class assumptions, instead of which he was just up against a dusty and illogical old law. A law can be changed with relative ease, but class prejudice can't, and isn't that what Jimmy McGovern is supposed to be about?