Inmarsat, the UK-listed satellite communications provider has received a takeover offer from Harbinger Capital, the activist American hedge fund investor.There is no certainty that a formal bid will be made soon, as Harbinger believes that obtaining regulatory approval from the Federal Communications Commission could take up to 18 months.Harbinger has a 29.9 per cent stake in Inmarsat, and is thought likely to approach the American industry watchdog now that its intention has been made public.