A Suffolk poultry plant is among more facilities owned by the UK's biggest supplier of supermarket chicken to be inspected amid food safety and hygiene concerns within the company.

2 Sisters Food Group is the subject of an investigation by the Food Standards Agency (FSA) after undercover reporters claimed to have found potential food safety breaches at its West Midlands plant.

Despite finding no issues at the plant in West Bromwich, the FSA has announced it is extending its investigation to 12 other 2 Sisters facilities – including one at Flixton, near Bungay.

An FSA spokesman said the plant, which employs 650 permanent staff, was being inspected rather than investigated – a lower level of examination.

They also confirmed the group's other East Anglian processing facility, in Thetford, is not among the sites being inspected.

2 Sisters suspended production at its West Bromwich plant following an investigation by the Guardian and ITV which alleged that use-by dates and source codes on chicken had been altered.

The FSA said that while no food safety issues were identified at the plant, its inspection 'highlighted issues requiring management attention' around staff training and stock control.

After the allegations surfaced, Tesco, Sainsbury's, Co-op, Marks & Spencer, Aldi and Lidl announced they would stop taking orders from the plant – but said this boycott would not extend to other 2 Sisters facilities.

An FSA spokesman said: 'We are working with the major retailers supplied by 2 Sisters, as well as reviewing information from various other sources.'

Following the decision to expand the investigation, FSA chairman Heather Hancock 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.

A 2 Sisters Food Group spokesman said: 'We receive regular audits at all our English and Welsh sites by the Food Standards Agency (FSA) throughout the year, so of course we will welcome our FSA colleagues at any location they wish to inspect in the coming days.'

NFU East Anglia adviser John Newton said the organisation was aware of the FSA's inspections at other 2 Sisters poultry plants.

He said: 'The NFU is continuing to monitor the situation, while awaiting the findings of this investigation.

'Our members are rightly proud of the high standards they work to and it is absolutely vital that these are replicated throughout the supply chain.'