Security guards have been posted at Clays and staff at the book printer, a member of the huge St Ives printing group, have also been forbidden from using mobile phones lest they may be tempted to use them to photograph pages from the book.
Meanwhile, Harry Potter author, J K Rowling and publisher, Bloomsbury, are appealing to anyone who knows anything about the plot to keep it to themselves to avoid spoiling the book for others.
In 2003, Donald Parfitt, 44, a forklift driver at Clays was sacked later and sentenced to 180 hours of community service after admitting to stealing pages of Harry Potter And The Order Of The Phoenix.
Parfitt had claimed to haved found the pages in the Clays car park but an attempt was later made to sell them to a newspaper.
This time around, Clays staff are working with greater restrictions in a stepped-up effort to prevent any details about the highly-anticipated book from leaking out.
Staff have had to sign a contract banning them from talking about the book with family or friends and workers who normally scan-read books for errors have been banned from doing so.
Harry Potter and the Deathly Hallows, in which one of the main characters dies, is the most ordered book in history.
