Almost 300 people have tested positive for Covid-19 following an outbreak at a factory which makes M&S sandwiches.
Greencore in Northampton started “proactively testing” workers due to rising numbers of cases in the town.
Lucy Wightman, Director of Public Health at Northamptonshire County Council, said 299 workers had tested positive.
A spokesman for the company, which employs 2,100 people, said those who tested positive were self-isolating.
He added that in each case it had “conducted contact tracing”.
Mrs Wightman said 220 people had tested positive as part of Greencore’s testing and another 79 “through the national process” and all were employees at the site.
Northampton had already been identified as potentially facing a local lockdown.
The number of confirmed coronavirus cases in the town increased from 67 in the week ending 1 August up to 85 for the week ending 8 August.
One of those to test positive was Bakers’ Union’s branch secretary for the factory, Nicolae Macari.
He said he tested positive on 4 August, along with his mother and father - who also work at Greencore - and his wife.
“When suddenly three or four people are pulled out of a line because they have tested positive, people are terrified,” he said.
Mrs Wightman said Greencore had “highly effective measures in place and they continue to work extremely hard to exceed the requirements needed to be Covid-19 secure within the workplace”.
She said the outbreak was “about how people behave outside of Greencore, not at work,” adding if people failed to follow the rules “a possible local lockdown will follow”.
Greencore said production at the plant was “continuing as usual” and it had no concerns about its products.