High street coffee shop giant Starbucks has been caught up in a child labour row after an investigation revealed that children under 13 were working on farms in Guatemala that supply the chain with its beans.

Channel 4’s Dispatches filmed the children working 40-hour weeks in gruelling conditions, picking coffee for a daily wage little more than the price of a latte. The beans are also supplied to Nespresso, owned by Nestlé. Last week, actor George Clooney, the advertising face of Nespresso, praised the investigation and said he was saddened by its findings.

The Dispatches team said some of the children, who worked around eight hours a day, six days a week, looked as young as eight. They were paid depending on the weight of beans they picked, with sacks weighing up to 45kg. Typically, a child would earn less than £5 a day, although sometimes it could be as low as 31p an hour.

Over the course of the investigation, Dispatches visited seven farms linked to Nespresso and five linked to Starbucks. Child labour was found on all the farms.

A human rights lawyer who viewed some of the programme’s evidence suggested both companies were in breach of international labour regulations laid down by the UN’s International Labour Organization.

“The conventions are very clear in that they don’t want children’s education to be compromised,” said Oliver Holland of solicitors Leigh Day. “If children are working 40 hours a week, there is no way they can also be having a proper education.

“These are all unsafe conditions for children essentially, and in those conditions children simply shouldn’t be working.”