The licence fee payer is the loser from the multi-million-pound trade. By maintaining the fiction that “brand placement” agencies are no more than tradesmen supplying props, the BBC can fend off pressure to sell conventional advertising. But for relatively paltry benefits in kind it hands over promotional slots worth thousands of pounds.

Some product placement agencies influence editorial content. An agent persuaded the BBC to use a Sony PlayStation game on the mystery guest slot of A Question of Sport. It featured Lawrence Dallaglio.

The BBC editorial guidelines state there should be no product placement but do allow the use of some brand names to convey realism. In “rare cases” these can be provided free of charge.

In fact this clause has been exploited to spawn an industry of product placement agencies, although the BBC does not gain a direct cash benefit.

Placement with stars is most prized: Ricky Gervais holds a Benjys coffee cup in Extras on BBC2 and Robert Lindsay clutches a bottle of Sol beer in My Family, a BBC1 comedy.

A new prime-time BBC2 series, The Hairy Bikers’ Cookbook, has become a target for the placement agencies. The reporters spoke to the programme’s maker offering to pay its travel and accommodation costs on location.

In return they asked that our fictitious drink — a Mexican beer called Reds — was shown on the programme. John Stroud, managing director of Big Bear Films, said: “I don’t see a problem with that.”

Malcolm Holt, the prop master for Hotel Babylon, was also happy to support the product. “I can do you two or three bottles on the bar — prominent, all the time,” he said.

The BBC said that it would investigate the allegations.