In September the police launched an investigation into the possible deliberate contamination of bread after glass, sewing needles and chewing gum were found in packs of Kingsmill.
The 400-strong workforce was asked to volunteer for DNA and fingerprint testing in October. The police tactic was supported by union reps and staff were co-operative. But no suspects have been identified.
Allied Bakeries has stepped up security at Orpington and there have been no further instances of contamination.