The Norwegian company, Statoil, says it will not accept delivery of a rig built at the yard because the work has not been completed to its satisfaction.

A Statoil spokesman would not be drawn on specific details but said the complaints related to "safety and structural considerations".

The Scandinavian owners of Harland & Wolff, Olson Energy, had contracted to supply the rig to Statoil.

The vessel was built but was a year behind schedule and went over budget.

The latest row comes as Harland & Wolff seeks to resolve another row over its only other major order.

American company Global Marine says it will not pay several million pounds which Harland & Wolff claim is owed over work carried out on an oil exploration vessel.

The row with Global Marine also puts a question mark over an order for two other vessels from that firm.

Union official George Matchett has expressed concern over the timing of the latest row but is hopeful that the matter can be resolved.

"It's disappointing that it's come at this time, particularly as we've been having the discussions with Global.

"Those discussions are currently taking place in London where I believe Harlands are presenting a very detailed and strong case," he said.