Allied Bakeries informed the police and the UK's food agency of deliberate contamination of its Kingsmill sliced bread, of which 2.5 million loaves are produced each week, with glass or sewing needles.
For the moment, there is no recall on the cards.
"The risk assessment has been done at the Kent plant, and it was decided that at this stage we would not carry out a recall," confirmed a spokesperson at Allied Bakeries.
He told FoodNavigator.com that the firm had received five complaints of "quite a serious nature", sparking the move to contact the police and the Food Standards Agency (FSA).
According to Allied Bakeries the foreign objects were clearly visible once the bread bag was opened, and were not embedded in the bread.
The investigation work must shed light on whether the harmful ingredients contaminated the products at the plant, or once they had left the Orpington plant in Kent.
The firm said it has increased security in Orpington in a bid to minimise risk.
The Orpington bakery distributes to retailers across the South East of England, including Iceland, Londis, Sainsbury's, Spar and Tesco.
To date, no reports of foreign objects had been found in bread sold by these retailers under their own labels.
According to to Allied Bakeries, this is the first cluster of such complaints from Orpington plant.