The owner of the unit on the Bellbrook Estate, Mr Kevin Benton, reckons there are between 6,000 and 8,000 NHS test pots, carrying patient information, including addresses, dates of birth, and telephone numbers.
The business that occupied the unit has gone into administration.
A spokesperson for High Weald Lewes Havens Clinical Commissioning Group said: “As the local commissioners of health services for the Uckfield area, we are investigating on behalf of the NHS.
“The NHS takes patient safety and confidentiality extremely seriously and, once we fully understand what the situation is, we will ensure necessary action is taken.”
An expert has also identified dangerous chemicals in the unit. Read more in the stories linked to below.