The decision follows an investigation into practices at the 2 Sisters Food Group’s plant at West Bromwich in the West Midlands in the light of concerns raised by ITN/Guardian at the end of last month.
Although the FSA inspection, which was carried out with the local health authority, did not identify food safety issues, it did highlight issues requiring management attention. These include aspects of staff training and stock control.
Plants now being investigated are believed to include Devon, Scunthorpe, Basildon and Anglesey in Wales.
The FSA said it was working with major retailers supplied by 2 Sisters as well as reviewing information from various other sources.
It has also written formally to ITN and the Guardian to request the full evidence taken by their undercover investigation, such as the footage taken and witness interview transcripts.
Heather Hancock, FSA chair, said: “Consumers deserve food they can trust, and can be reassured that we take allegations of poor practice very seriously.
“Although our initial inspection found no risk to public health, we are broadening our investigations until we are satisfied that this is truly the case.
“I’m disappointed that ITN and the Guardian have not yet provided the information that they committed to share and I would urge anyone who has evidence to share to bring it directly to us,” she added.
A spokesman for 2 Sisters told the Telegraph that it welcomed FSA colleagues at any location they wished to inspect in the coming days.
“We are continuing to support our colleagues during our retraining period and we remain committed to ensuring that we operate to the highest standards of hygiene and food safety, and we act with honesty and integrity at all times.”
• Meanwhile, the owner of 2 Sisters Food Group, Ranjit Singh Boparan was said to be in talks to merge his Fox’s Biscuits brand with Burton’s Foods in the hope of listing the enlarged entity on the London Stock Exchange, according to Sky News.