It has partnered with a consortium that includes an Australian fund manager and Singapore’s electricity distributor to enter the auction for the business which is expected to be valued at £11 billion.
First-round bids for a 51 per cent stake were due on Friday with the sale process expected to last several weeks.
However, energy worker union GMB has called for a halt to “yet another example… of fundamental UK infrastructure being flogged off to the highest foreign bidder” until the government has completed its promised review of the Enterprise Act.
GMB said the business “is not a cash cow but a key piece of infrastructure, vital to our economy” which should be subject to the same checks the Hinkley Point C project underwent before the government gave final approval.
The government intends to review the 2002 Enterprise Act to see whether infrastructure should be added to the sectors in which ministers can intervene.
GMB national secretary for energy Justin Bowden said: “Theresa May should intervene and put this sale on hold until the review of the Enterprise Act is completed and there are proper safeguards in place.
“If it was good enough in her opinion to delay the go-ahead to Hinkley Point, then it is certainly good enough to put the brakes on here.”