BP faces up to four months further delay before it produces the first oil from its pioneering development west of Shetland.
The latest setback on the Foinaven project follows the failure of one of the two underwater production manifolds during testing and will mean production starting almost a year later than planned.
While BP managed to stop leaks from four of the manifold’s 48 valves during the pressure test, it said it would remove the unit from the seabed for inspection and repair.
While the cause of failure cannot be ascertained until the manifold is brought to the surface, it is thought that Teflon seals surrounding the valves may have been distorted during installation.
Despite the latest delay, BP said Foinaven would still have gone from discovery to first oil in five years, against a historical average of eight.