Shares in Inmarsat, the mobile satellite communications group, plunged 12.2 per cent today after it emerged that Harbinger Capital, the activist American hedge fund investor, has suspended talks over a possible takeover.

While both parties left the door open to a future deal, Inmarsat's stock lost 62.75p to fall to 449.75p in early trading.

Harbinger, which owns 28 per cent of Inmarsat, has put talks on hold to consider the lengthy regulation involved in such a deal, which could take up to 18 months.

The hedge fund would have to gain clearance from the Federal Communications Commission, the US industry watchdog that oversees the sector in a similar way to Ofcom in Britain.

The group said: “Harbinger remains interested in acquiring control of Inmarsat and is therefore actively considering whether to pursue the relevant regulatory and competition approvals in order to be able to make an offer for Inmarsat in the future.

“Assuming there is an acceptable conclusion to the regulatory approval process, Harbinger would intend to re-enter into discussions with the board of Inmarsat regarding the terms of an offer and endeavour to seek a recommendation from the Inmarsat board at that time.”

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 is run by Philip Falcone, a former trader at Barclays Capital, and operates funds under management of $26.5 billion (£13.4 billion) as at the end of June.

Harbinger is one of a handful of hedge funds to have piled into the satellite group’s shares in recent months. Funds run by Lansdowne Partners and Lehman Brothers have also been big buyers in anticipation of consolidation in the industry.

Harbinger, which owns stakes in SkyTerra and Terrestar, both rival operators, is also attracted by the prospective role that Inmarsat might play in the development of a satellite-based mobile phone network in the US.

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