Nick Broomfield takes a rare break from documentaries with this careful and utterly convincing reconstruction of the tragedy that drowned 23 cockle-pickers in Morecambe Bay three years ago. It starts and finishes with the waves rushing in in near-darkness. Anyone who has been cut off by the tide knows what a scary sound that is. In between times we follow survivor Ai Qin Lin's journey from China to try to find work to pay for her child's education.

At first the gang of illegals brought in are preparing meat and picking fruit and vegetables for supermarkets, living in Norfolk. But after a police raid, the ones still at liberty head north to pick up cockles. Why would they be stupid enough to do it at night? Because the locals, understandably annoyed by the illegal intrusion, have beaten them up and stolen their cockles when they worked by day. Together with Last Resort, In This World and Dirty Pretty Things, British cinema has impressively cast a light on the plight of the illegal immigrant and the dangers they face.

The Chinese have been victime of two tragedies as Winterbottom's In This World arose from the story of more unfortunates who suffocated on a lorry in Dover. It's not all grim and miserable - Broomfield allows for some camaraderie and humour along the way, though you can't help wincing when his travellers see a rainbow over Morecambe as a good omen for their future. Broomfield's film, which made use of undercover research by Guardian journalist Hsiao-Hung Pai, is so impressive, you hope he'll do more non-documentaries, while his only fiction film I've seen, Diamond Skulls, had quite the opposite effect. The term Ghosts, by the way, refers both to the Oriental colloquial term for pale-faced westerners as well as the unseen part of the black economy and to the spirits who departed this world on a wet Lancashire night.