Agit-prop documentarian Greenwald has previously turned his sights on Fox News in Outfoxed: Rupert Murdoch's War on Journalism and the legality of war in Iraq with Uncovered: The War on Iraq.

So you know his dissection of the Wal-Mart corporation will not be pretty.

Even allowing for filmmaker bias, the catalogue of evidence is overwhelming. Toxic waste dumping, union busting, below poverty-level wages, racism, exploitation of illegal immigrants, funding dictatorial Third World bullyboys: Greenwald presents a shopping list of injustices.

Using dozens of interviews with ex-employees, TV clips, Wal-Mart's own corporate videos (including a propaganda piece on the evil of unions), the film mounts an impassioned plea for federal control of this almost comically evil empire, while ruefully pointing out that while states are closing schools they are also awarding subsidies to Wal-Mart stores.

The victims are Wal-Mart employees around the world, small business owners who cannot compete with those low prices and shoppers who face possible rape and murder in store car parks - one galling scene recounts a woman's assault at a Wal-Mart that had no cameras monitoring the car park but hundreds watching the customers inside the store.

The company's damaging business practices extend further than the 50 states, and Greenwald succeeds in painting a picture of global corruption, from China where slave-wage workers have utility costs docked from their pay, to Germany, to England.

Wal-Mart is the proud owner of Asda (chillingly, the lowest priced supermarket eight years in a row according to Sharon Osbourne), and a segment on London market traders fighting Asda plans to buy up their pitches literally brings home how threatening Wal-Mart is to everyday life.

Slow to start, once Greenwald's film hits its stride it grips the attention, being a horror film, black comedy, social tragedy and tearjerker.

Wal-Mart: The High Cost Low Price will change the way you shop.

Rob Daniel