The Iranian Oil Company has been allowed to resume production in the huge Rhum North Sea gas field after the British government removed a ban on it.
The field, which is co-owned by British Petroleum and the Iranian Oil Company in a joint venture, was shut in 2010.
The IOC was banned in accordance with European Union sanctions against Iranian firms.
In a statement the government said that it supports restarting production at Rhum, which is necessary to avoid potential environmental damage and to prevent the possible destruction of the value of the field.
BP said it was too early to say when production at the field could resume.
"We look forward to receiving final authorisation over the next few weeks, which will enable us to start work towards restarting the field," a BP spokesman said.
The Rhum gas field was contributing around 4% to UK gas production in October 2010 before its shutdown.
It started pumping gas in December 2005 and cost £350m ($565.6m, €410.7m) to build.
EU sanctions against Iranian companies, including the IOC, are still in place, and the British government said the IOC's revenue from gas sales at Rhum will be placed into a frozen account.
Sanctions on Iranian companies were imposed three years ago by the United States and EU, alleging that Iran is trying to develop nuclear weapons. Tehran says its research has purely peaceful, civilian aims.