Marks & Spencer, Aldi and Lidl have all suspended buying chicken from one of the UK's largest suppliers after an investigation allegedly revealed a string of health and safety breaches.

An undercover reporter working at a West Midlands site of the 2 Sisters Food Group (2SFG) claimed to witness workers tampering with slaughter dates and mixing meat of different ages.

Source codes on crates of meat were also changed, the investigation by ITV News and the Guardian claimed.

The practices can artificially extend the shelf life of meat, and make it untraceable in the event of an outbreak of food poisoning.

When meats of different ages were mixed together, the slaughter date of the newest batch rather than the oldest batch would be used, employees claimed.

Some workers also claimed the chicken that supermarkets reject is sometimes repackaged at the factory and sent out again.

Quality assurance workers told journalists they were intimidated by production managers and worry about being sent home if they try to enforce food hygiene rules.

A spokesman for Lidl said: "Lidl UK takes the issue of food safety extremely seriously and we were very disappointed to see the unacceptable standards shown in yesterday's report.

"We immediately launched an investigation with the supplier and can confirm that we will not be sourcing from the site until the investigations have been satisfactorily concluded."

Aldi added: "We have suspended supply from this site while we carry out an urgent investigation into these allegations.

"We expect all suppliers to adhere to the highest possible food hygiene and traceability standards at all times."

M&S said it had also suspended business with 2SFG, pending the outcome of an investigation.

A spokesman said: "As a precautionary measure, all fresh chicken that is supplied directly from this site has been removed from our shelves today."