The proteins make the skin transparent and give off a greenish glow when exposed to certain ultraviolet light. Typically, they are used to monitor the activity of altered genes, and in this case to monitor transplants for heart disease.

The lamb belonged to the Inra’s animal research unit, UECA, which sells its unmodified animals to a local abattoir but has strictly no right to sell GM animals.

An internal investigation into the huge slip-up suggests foul play on the part of an employee acting out of revenge after a dispute with a colleague.

While Rubis was a class 1 GMO, in other words containing a gene posing “no or negligible risk” to humans, Gérard Pascal, a former Inra biochemist, told Le Parisien its introduction into the human food chain was “intolerable”.

“Beyond the ethical issues, one cannot put foodstuffs into the market that haven’t been the subject of deep research. Until they’ve been studied, one cannot assess the risk,” he said.

A judicial source said: “This affair seems unbelievable and threatens to do harm to an institute that is renowned for its seriousness. But it also shows, if the facts prove correct, that the best-controlled institution cannot ward against individual waywardness.”

Benoit Malpaux of Inra said the culprits would be punished. “This is unacceptable and calls for the utmost severity. We are a world-renowned institute. We cannot tolerate such acts.”

He said: “Normally the animals are euthanised and their carcasses incinerated.”

The charge of “placing on the market a genetically modified product or containing such organisms” carries a maximum year’s prison sentence and €75,000 fine.

Henry Samuel