Murco’s US parent business is set to sell its UK business next month to a private equity firm for more than $500m, according to sources close to the negotiations.

Murphy Oil has had a long-stated aim of selling off its UK business and two weeks ago a spokeswoman confirmed: “Discussions with regard to the sale of the Murco UK business by its US parent, Murphy Oil Corporation, are ongoing and are at an advanced stage.”

The sale would include the petrol station business and its Milford Haven refinery in Wales.

The buyer is believed to be a London-based private equity group, Greybull Capital, and it is reported to have agreed to fund a major planned maintenance at Milford Haven within the next 18 months.

Greybull declined to comment on the discussions.