The UK considered changing its merger control regime this year to block a potential takeover of Centrica, the UK’s biggest gas supplier, by Gazprom of Russia, a move that remains an option to thwart any bid that threatens energy security.

Alan Johnson, the trade and industry secretary who has been a vocal critic of protectionism in the US and Europe, was briefed with other ministers in February on the legal changes required to allow them to block a rumoured bid by Gazprom for Centrica, the Financial Times has learnt.