Russian billionaire Mikhail Fridman has been given seven days to justify why he should be allowed to retain ownership of newly bought oil and gas fields in the North Sea.
His investment fund LetterOne bought 12 oil and gas fields from German utility RWE, which was finalised earlier this week.
The deal went ahead despite objections from the UK Government.
Britain’s Energy Secretary Ed Davey has written to Mr Fridman, giving him a deadline to convince the UK Government not to force him to sell the oil and gas assets.
It has been suggested the government has concerns production at the fields could stop if the west imposes more sanctions on Russia over Ukraine.
“Ed Davey has given them seven days to explain why the Secretary of State should not now proceed to issue Notices under the Licences to require further changes of control. Protecting these assets is the Secretary of State’s priority,” DECC said in a statement.
As part of the deal, LetterOne plans to create a new subsidiary, L1 Energy, which is to be run by former BP Chief Executive Lord Browne.