A cooling tower at the firm's Pershore site tested positive for the bacteria just before the Christmas break, sparking concern among staff.

Managing director Ian Gibson said the outbreak had been identified and dealt with quickly, due to the firm's stringent checks.

However, he said an investigation was being carried out to ascertain the cause. The firm has confirmed no employees contracted the disease.

- Meanwhile, the firm's Purnell factory in Somerset closed after the last shift on New Year's Eve.

Some 28 staff will remain at the Paulton site until the final decommissioning in March.