In a statement issued this morning (7 September), De La Rue said its ongoing investigation into the "serious" production problems at the Overton mill revealed that some of its employees had "deliberately falsified" certain banknote paper specification test certificates for a "limited number of customers".

Further to its investigation, De La Rue discovered that a small number of banknote papers had "fallen marginally short" of the specification. This resulted in the board stopping shipment of the affected banknote paper.

Nicholas Brookes, executive chairman of De La Rue, said: "The behaviour of some of our employees in this matter was totally unacceptable and contravened De La Rue's rigorous standards. We do not tolerate such behaviour and appropriate disciplinary action is being taken."

The damaging revelation, which sparked a 9% fall in the company's share price to 638.5p, has led to another two high-profile departures in Mark Jeffery and Jonathan Garside, manufacturing and sales directors respectively of the group's currency division.

Their exit follows the resignation of former chief executive and managing director of the currency division, James Hussey, who stepped down last month after taking responsibility for the group's paper production problems.

De La Rue has now appointed Keith Brown as the new managing director of the division.

Meanwhile, De La Rue is being assisted in its investigation by its external legal advisers and has reported its findings to the relevant law enforcement agencies.

While the group has not been able to quantify the scale of the damage to its full-year results for the current and subsequent years, it said the adverse financial impact on first-half pre-tax profit would likely be "at least £35m".

This has been attributed to one-off costs, including stock write-offs, professional fees, rectification and production trial costs, as well as some "slippage" of currency volumes in the second half.

All production is now within specification and the company is ready to resume supply of fully compliant paper, while De La Rue remains confident that neither the physical security nor the security features in the paper have been compromised.

Brookes added that the board was continuing to carry out a very thorough investigation and was keeping De La Rue's customers and the legal authorities fully informed.

"The company reiterates that it has not found anything to suggest that either the physical security or the security features in the paper have been compromised and that the matters uncovered relate only to the certification of paper specifications at the relevant facility," he said.

Unite assistant general secretary Tony Burke said the news was of great concern and could lead to disciplinary action against some staff, in which Unite may have to represent its members.