Prior to a trading suspension Atos Origin stock rose as much as 29.6% to EUR51.25 - the biggest gain in over 10 years - on the back of news reports that the group had received a EUR4 billion approach from equity firm Permira Holdings and hedge fund Centaurus Capital.

According to a Reuters report, which cites a source familiar with the matter, the talks may lead to an offer of EUR58 per share, which represents a 47% premium to the share's closing price on Wednesday.

Shares were eventually suspended at the request of Atos Origin, pending a statement which admits that the firm had received "expressions of interest" but states that it is not "engaged in any financial operation with respect to its share capital".

But the Reuters report says "talks continue and may yet fall through" and although the discussions have not yet led to a firm offer they are "serious".

But in its statement Atos says it is "is focused on the execution of its transformation plan approved by the supervisory board and presented to the market, which is value enhancing".

Centaurus and Permira have have so far declined to comment on the rumours.

This is the second time in six months that Atos had denied reports of a takeover offer. In October the vendor denied reports that it was in takeover talks with US private equity firm Blackstone.

Atos Origin provides IT services to multi-national clients in targeted industry sectors.

Earlier this week the firm's Atos Euronext Market Solutions unit, a 50:50 joint venture established with Euronext, parted ways with its chief executive and chairman Jean-Marc Bouhelier following disagreements over the strategic direction of the company.

Bouhelier - a former chief operating officer of Instinet - was named head of AEMS in July 2005. But he has now been replaced with Philippe Germond, a member of the Atos Origin management board. Francis Delacourt has been appointed deputy chairman.

AEMS is expected to play a key role in the integration of Euronext with merger partner The New York Stock Exchange.