Incidents of alleged tampering have dogged the site since last summer, with sewing needles, glass and chewing gum found in packs of Kingsmill bread.
To date there have been 35 reported contaminations, but the last was reported in January.
A spokesman for the Metropolitan Police said three further incidents were reported last week - two involving glass and one involving a needle. No arrests had been made and inquiries were continuing.
A bakery spokeswoman said: "Allied Bakeries is working with the Food Standards Agency and the Metropolitan Police. We continue to take all necessary action to ensure our products are safe."