Internationally famous satellite operator Inmarsat said on Monday that it had received a preliminary approach made on behalf of funds managed by Harbinger Capital Partners that may or may not lead to an offer. The news sent its shares rising the maximum in six months, effectively valuing the company at £2.41 billion ($4.75 billion).

The stock jumped as much as 10 per cent after Harbinger's admission ended months of speculation. Shares closed up 30 p, 6 per cent higher at 525p, adding almost £140 million to Inmarsat's market value. The shares have fallen 3.3 per cent this year.

Inmarsat received a ''very preliminary approach'' from Harbinger that ''may or may not lead to an offer,'' the London-based company said in a statement. Separately, Harbinger Capital Partners Funds confirmed the approach and said it is in the initial stages of assessing Inmarsat.

''No decision has been made regarding the merits or otherwise of a possible offer. Furthermore, a lengthy regulatory approval process would be required to effect an offer,'' it said, adding that a further announcement may be made if and when appropriate.

If it wanted to pursue a takeover, Harbinger would have to gain clearance from the Federal Communications Commission, the American industry watchdog that oversees the sector in a similar way to Ofcom in Britain.

This process could take up to 18 months. Banking sources suggested that Inmarsat might be able to apply to the UK Takeover Panel for an exemption, which would mean that it would not remain in an offer period for the entire time.

Harbinger, which has accumulated a 29.9 per cent stake in Inmarsat, is likely to approach the American regulator in the coming days now that its interest has been made public.

Inmarsat has benefited from higher sales to the maritime and aviation industries, providing mobile Internet, safety, rescue, weather and mapping services. A sale to Harbinger would put the company back into private ownership after its £367.5 million initial public offering in June 2005.

Sales at Inmarsat climbed 15 per cent to $576.5 million in 2007. While profit fell 24 per cent in the year on higher taxes, operating profit jumped 15 per cent to a record.

Inmarsat plc is an international telecommunications company founded in 1979, originally as an intergovernmental organization. It operates a fleet of eleven geosynchronous telecommunications satellites. The company is publicly traded on the London Stock Exchange as of December 2007.

Inmarsat was originally founded as the International Maritime Satellite Organization (IMSO) as a not-for-profit international organization in 1979, at the behest of the International Maritime Organization ("IMO", a UN body) for the purpose of establishing a satellite communications network for the maritime community.

From the beginning the acronym "Inmarsat" was used. The intent was to create a self-financing body that would improve safety of life at sea. The name was changed to International Mobile Satellite Organization when it began to provide services to aircraft and portable users, but the acronym "Inmarsat" was kept.

When the organization was corporatized, the company was split into two parts: the bulk of the organization was converted into the commercial company Inmarsat plc, and a small group became the regulatory body IMSO. In spite of the commercial structure, Inmarsat has maintained its traditional multicultural atmosphere of some 45 nationalities in the London headquarters. Inmarsat continues to ensure it meets the requirements of a Global Maritime Distress and Safety System (GMDSS) as established by the IMO.

Inmarsat provides telephony and data services to users worldwide, via special terminals. An Inmarsat terminal contacts the satellite and communicates to a ground station through the satellite. It provides reliable communications services to a range of governments, aid agencies, media outlets and businesses needing to communicate in remote regions or where there is no reliable terrestrial network.

Harbinger is run by Philip Falcone, a former trader at Barclays Capital, and operates funds under management of $26.5 billion (£13.4 billion) as of the end of June. It was forced to admit that it was lining up a potential offer after it emerged that Harbinger had hired Merrill Lynch, the American investment bank, to review the possibility of a bid. Merrill has a longstanding relationship with Harbinger in the US, but this is the first time that the bank has advised it on a European deal.

Sources close to the fund said that Harbinger wanted ''to take control of the company, just like a traditional strategic buyer''.