Royal Dutch Shell’s ￡55bn bid for BG Group faces any number of hurdles, including volatile oil prices and the risk of a counterbid, but the biggest of all may prove to be what one competition lawyer calls the “black box” that is China’s Ministry of Commerce, the country’s opaque antitrust regulator.

Regulatory scrutiny of the deal — the biggest in the energy sector for more than a decade — will take months. Competition authorities in Australia, Brazil, China and Brussels are among those expected to examine the size and reach of the combined company, which is set to be the world’s biggest supplier of liquefied natural gas.

Some could wave it through with minimum fuss. For the European Commission, traditionally more sensitive to the impact on prices for consumers, the BG takeover is regarded as unlikely to raise the concerns that a “downstream” merger, between say Shell and BP, might.