Harbinger Capital, which owns about 28pc of Inmarsat and is run by Philip Falcone, is understood to be considering a sale after it received several approaches from investors who want to acquire some or all of the shareholding.
However, Harbinger has not yet made a final decision on whether it should dispose of its stake, said people familiar with the matter. Harbinger – which in 2008 tried to buy Inmarsat – declined to comment. Inmarsat edged up 5 to 668½p.
Overall, the FTSE 100 climbed 44.28 points to 5592.90 and the FTSE 250 rose 60.67 points to 10592.47.
News that Sinopec is to invest $7.1bn (£4.5bn) in Repsol's Brazilian unit helped BG Group top the blue-chip leaderboard. BG Group which has extensive oil and gas interest in Brazil, put on 51½p to £11.70. There was also some talk in the market that Royal Dutch Shell, up 31p to £18.88, could be preparing a bid for BG Group.
Tullow Oil, meanwhile, gained 34p to £13.08. Traders reckon the company is a target for Sinopec or CNOOC, two state-backed Chinese organisations.
BP advanced 12.7 to 440½p as TNK-BP was rumoured to have made an offer for the London-listed group's Venezuelan and Vietnamese assets. ?
In the mining sector, Fresnillo increased 28p to £12.70 after JP Morgan Cazenove upgraded the stock to "neutral". David Butler, an analyst at the broker, is relatively bullish about the prospects for gold and silver prices. This is because very low US and European central bank rates have yet to translate into decisive economic growth figures but are fuelling fears that inflationary conditions are being created.
Mr Butler added that low yields on government debt in combination with high government deficits have encouraged money to flow into gold-backed exchange-traded funds. JP Morgan Cazenove also lifted its price target on African Barrick Gold, up 9½ to 599½p, to 900p from 755p. Elsewhere in the sector, Randgold Resources moved 155p higher to £65.25.
BT Group rose 2.8 to 142.8p as JP Morgan Cazenove said it sees the pension issues facing the company as a "reducing concern". "Given the numbers involved, this is very material for BT's equity value and underpins our overweight recommendation," said Paul Howard, an analyst at the broker.
Amec climbed 24p to £10.10 as Credit Suisse took up coverage with an "outperform" rating and a price target of £11.80. Analysts at Credit Suisse said: "Amec is poised to benefit from exposure to significant areas of upcoming capex [capital expenditure] growth in Canadian oil sands, mining and nuclear. We think this theme of defensive, reasonably-priced growth driven by a recovery in energy spend is compelling in the context of an uncertain outlook for the general economy."
Goldman Sachs put HSBC on to its "conviction buy" list, which helped the shares put on 8.6 to 653.6p.
On the mid-cap index, Brewin Dolphin surged 10¾ to 142½p after it said in a pre-close statement that assets under management have and the group has experienced strong levels of trading commission during the fourth quarter.
Spectris rallied 11p to £10.84 following its acquisition of N-TRON, a privately-owned US manufacturer of rugged industrial networking components, for $51m (£32m).
However, CSR fell 14.6 to 344.4p as several brokers downgraded the technology company. Exane BNP Paribas, for example, downgraded the shares to "underperform".
Small-cap Asterand jumped ¼ to 12¼p after it said it had won a $24.3m five-year contract with the National Cancer Institute to supply clinically annotated human biospecimens for The Cancer Genome Atlas project.