A BBC documentary has sparked an investigation by supermarkets into hygiene practices at a number of Welsh abattoirs after it showed faecal contamination on meat that had been health-marked.
Journalists secretly filmed alongside meat hygiene inspectors and discovered approved carcases were affected. While the BBC report said there was no suggestion that the meat reached the public, three supermarkets have launched inquiries.
It has also led to a call for an investigation into how the Meat Hygiene Service (MHS) polices the industry.
BBC journalists for the Week in Week Out programme posed as prospective veterinary students for the special investigation.
Secretly filming alongside Meat Hygiene Service inspectors and vets, they found carcasses which had been health-marked by inspectors still contaminated by faeces. .
The programme's findings have led the man chairing the public inquiry into the 2005 E.coli outbreak in south Wales to question the role of the MHS.
Prof Hugh Pennington said on BBC Radio Wales this morning: "We are very good at learning lessons, but we are even better at forgetting them.
"Events like the 2005 outbreak in Wales, you would expect that would have an impact.
"I'm very disappointed that we seem to be going backwards rather than forwards."
Three abattoirs were visited, two in Carmarthenshire at Cig Calon Cymru in Cross Hands and Dunbia at Llanybydder, and HMD, a family run abattoir in Swansea.
Cig Calon Cymru supplies retailers including Somerfield and Marks and Spencer. Faecally contaminated meat was alleged by the BBC to have been found in the company's cutting room.
It also said there was no evidence to suggest that contaminated meat from Cig Calon Cymru's abattoir has been sold by M&S or Somerfield.
M&S said a "thorough auditing process" meant it was able to fully investigate the concerns.
A spokesperson for the retailer added: "We were able to act immediately to carry out a full investigation into the BBC's allegations, which showed that our supplier is operating to the standards we demand."
Somerfield confirmed that it suspended supplies of beef from Cig Calon Cymru and launched its own investigation, as well as issuing a product recall to customers.
At Dunbia, which supplies the supermarket Sainsburys, another journalist filmed a number of health marked carcasses still contaminated with faeces.
In a statement, the firm insisted that it always strives to achieve high standards, and was unaware of any current or past instances when MHS procedures were not followed.
The company added that its last MHS audit found "satisfactory performance" in all areas of the plant.
Again, there was no suggestion that contaminated meat was passed to customers by Sainsburys. The retailer is undertaking an inquiry into the allegations and said it works closely with suppliers to achieve the highest standards in food safety and quality.
Stuart Roberts, director of the British Meat Processors Association said that it was difficult for him to comment on footage which he had not seen.
But he added that even the most minimal contamination on carcases destined for the food chain was unacceptable .
Jane Downes, MHS veterinary and technical director, said: "We take very seriously any failure to maintain high standards in the meat industry. Our staff are highly trained and highly professional and we work closely with the Food Business Operator to ensure that meat is processed safely.
"We all have a responsiblity to minimise risk as much as we can. We have not yet seen the footage filmed in the documentary so we cannot make any further comment on the specific allegations".
* The Week in Week Out Special Investigation is on to be shown tonight at 20.30 on BBC One Wales.