The Competition & Markets Authority has brought the deal to the attention of the Secretary of State for Digital, Culture, Media & Sport as it may reduce competition in the market.
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Inmarsat agreed in March to be taken private by a consortium consisting of private equity firms Apax Partners of the UK and US-based Warburg Pincus, together with two Canadian pension schemes.
Completion of the deal had been pencilled in for around the end of the year, pending on regulatory approvals.
The CMA said on Tuesday that it was considering whether the transaction “will result in the creation of a relevant merger situation …[that] may be expected to result in a substantial lessening of competition” in the UK.
Comments on the transaction from any interested party have been invited, with a deadline for submission of July 29.
A deadline of September 10 has been set for an initial decision from the CMA.