According to Monday's Sun security cameras and 40 guards were scrutinising production at Arvato book printing subsidiary Druckerei GGP in East Germany.
A spokesman for Arvato parent Bertelsmann declined to comment on whether it had secured all or part of the print contract for Harry Potter and the Half-Blood Prince. However he did acknowledge that Bloomsbury was a major client.
St Ives Clays, which printed the previous Harry Potter books, was the subject of a media storm in 2003 when a forklift truck driver at the plant admitted stealing two first edition copies of Harry Potter and the Order of the Phoenix.
Donald Parfitt of Worlingham, Suffolk, had worked at the Bungay plant. He was handed a 180 hours community service order and ordered to pay 55 in costs in June 2003, after admitting trying to sell the copies to a national newspaper.
St Ives declined to comment, referring all queries back to publisher Bloomsbury. The loss of the contract for Harry Potter would be a blow to the firm.
Bloomsbury publicity director Katie Bond said that the publisher had no comment to make on the printing and distribution of the novel
prior to publication.
Harry Potter and the Half-Blood Prince is also set to become the first UK fiction book to be printed on Forest Stewardship Council (FSC) certified paper. The book is set for worldwide release on 16 July.
Story by Andy Scott
