De La Rue shares dived after it said the Serious Fraud Office (SFO) has opened an investigation into “suspected corruption” related to business in South Sudan.
The UK-headquartered passport and bank note manufacturer saw shares dive 12% after it informed investors about the investigation.
In a short update to shareholders, De La Rue said: “The UK Serious Fraud Office has informed De La Rue that it has opened an investigation into the De La Rue group and its associated persons in relation to suspected corruption in the conduct of business in South Sudan.
“Given the early stage of these matters, it is not possible to predict reliably what effect their outcome may have on De La Rue.”
It said that it intends to co-operate with the SFO in relation to the investigation and said it will provide a further update when appropriate.
De La Rue has worked in South Sudan since first designing and manufacturing a new currency for the country’s creation in 2011.
The Basingstoke-based printer has already had a turbulent month, after it came under pressure activist investors to axe its chairman Philip Rogerson.
Shareholders are due to vote on the future of Mr Rogerson, as well as executive pay, at the company’s annual general meeting on Thursday.
Last week, De La Rue hit out at Crystal Amber, its third-biggest investor, and described its threats against the chairman as “precipitous and destabilising” for the company.
The company is also in the midst of a leadership reshuffle after chief executive Martin Sutherland announced in May that he would quit the firm following a string of profit warnings.