The companies have been locked in a public war of words since Oberthur said it was interested in pursuing discussions that could lead to a bid following a torrid year for De La Rue, when production problems temporarily shut down a key facility.

De La Rue rejected an initial indicative offer of £895m by Oberthur, which then announced that it wanted more information on the state of De La Rue's relations with the Reserve Bank of India, believed to be the key client affected by the firm's paper production problem.

Earlier today (10 January), following representations from De La Rue's advisers, the UK Takeover Panel set a deadline of 5pm on 7 February for Oberthur to announce "a firm intention to make a bid", or to refrain from such activity for six months.

Oberthur responded within an hour, urging De La Rue's shareholders to pressure the company into divulging full details of its relationship with Reserve Bank of India as well as its prospects for gaining new customers in the light of its production problems and to thereby substantiate its claim that Oberthur's initial proposal did not reflect the fundamental value of De La Rue.

President Jean-Pierre Savare said that crucial questions "remain unanswered" ahead of what it described as a Put Up Shut Up deadline.

"Shareholders deserve a comprehensive update from [De La Rue] so that they can form a fully informed view as to the full financial impact of recent issues, the Company's standalone prospects, which we believe are uncertain, and the merits of our indicative proposal, which we believe offers compelling value, and act accordingly."

Shares in De La Rue opened slightly lower than Friday's close of 835p but surged back on the news, trading at roughly the same price at the time of writing.