Last night's Dispatches programme on exploitative labour practices painted another depressing picture of the price we pay for cheap food. The fact that such practices are commonplace in the groceries supply chain has been known for years yet two exposés in the space of a month – the first being The Guardian’s revelations that slave labourers are being used by Thai prawn producers selling to major UK retailers - shows that lessons are either not being learned or are being flagrantly ignored in the quest for ever cheaper produce.

Worker conditions, animal welfare and environmental impact are three key pillars of a sustainable food system that are all too often unaccounted for in the price we pay at the till. Consumers say they care about these things, and no doubt most do, but invariably they have neither the time nor the information at their disposal to check that every product they place in their basket has been produced ethically. The use of slave labour or exploitation of migrant labour is unacceptable and as the people that set the rules for participating in the groceries supply chain it is the responsibility of the retailers to stamp it out.

Supermarkets have the power to use standards as a way of excluding certain suppliers from the chain. They do it for fruit and vegetables through high specifications that often preclude smaller growers in the developing world from accessing value chains and so there's no excuse not to enforce the same standards for labour. To have rigorous standards over the appearance of fruit and veg and then turn a blind eye to the use of slave labour is not a tenable position. If the retailers can't reach an agreement to move as one to stamp out worker exploitation then the government must intervene to force them to do so. The worry is that the present government has little appetite to protect vulnerable workers. In fact, the recent Modern Slavery Bill failed to include a clause that would have placed new requirements on retailers to report any use of slavery in their supply chains, with the government instead preferring a voluntary approach.

Voluntary measures are all well and good but if some retailers pledge to crack down on exploitative labour practices and others don't then very soon those that are paying a premium for fair labour may find that consumers are punishing them at the till. It's almost inevitable that in a fiercely competitive environment where the big four are slashing prices to claw back share from the discounters that sooner or later standards will regress in the pursuit of ever lower prices. This can't be allowed to happen.

The problem with light touch regulation is that the burden lifted from businesses inevitably falls on those people with the weakest voice. Labour exploitation is a classic example. The horsemeat scandal was another; after all it wasn't supermarket executives buying those £1 ready meals. There should be no compromise. If the government and retailers don’t act decisively to clamp down on the use of slave labour and other exploitative practices we must assume they condone them. Fair and dignified employment is not a CSR-type ‘value’; it’s a basic human right.