Nuclear processing company Sellafield has launched an investigation into the loss of a USB stick containing information about the company's business operations.
The unencrypted stick was found in a hotel room in Cumbria by coach driver Craig Beavan.
It contained details of a proposed workforce transfer and information suggesting International Atomic Energy technicians visiting the site were not sufficiently briefed regarding health and safety regulations, said the Northwest Evening Mail.
A spokesman for Sellafield said no sensitive material was thought to be contained on the memory stick. "However, we take this issue very seriously and are investigating how this happened," he said.
Sellafield provides USB memory sticks to employees for transferring business-related information. All users of USB memory sticks are provided with guidance on their use, said the company.
However, Sean Glynn vice-president at data security firm Credant, said corporate USB sticks should always include encryption.
"Sellafield has done the right thing in launching an investigation, but this is a potentially serious breach of data security on several levels, with national security overtones," he added.