The logo is intended as a guarantee that the meat came from a British farm. But the tests, carried out by the British Pig Executive (BPEX) in order to demonstrate the accuracy of labelling, have in fact done the opposite.
When carried out on a packet of pork chops bought in Salford by a BBC reporter, they indicated that there was less than a one percent chance that the meat actually originated in the UK, with the most likely source being the Netherlands.
Tesco says it is extremely disappointed by the results. "When we specify that we want British pork, we expect to be supplied with British pork," a spokesperson says in a statement. "We have spoken with our supplier to make clear that this mistake is unacceptable."
The tests were based on Stable Isotope Ratio Analysis, which uses a database of four stable isotope ratios extracted from pork samples from known locations throughout the UK. BPEX formally introduced the new procedure today, and intends to carry out random testing four times a year.
Tesco says that all other tests have shown that products were correctly labelled, indicating that the cause may have been human error. But it's a big embarrassment for the company, which earlier this year vowed to tighten up its processes and introduce its own DNA testing across meat products.
"We want to leave customers in no doubt that we will do whatever it takes to ensure the quality of their food and that the food they buy is exactly what the label says it is," said group technical director Tim Smith at the time.
The company now says it's in talks with BPEX about incorporating the new isotope check into its internal test processes.