The Foreign Office confirmed that the two hostages had been liberated on Wednesday evening. Three other Britons were released earlier in the day.

The two have not been named, but are said to be "reasonably well".

The others - David Welch, 64, Keith Miller, 47, and David Shears - were also apparently unharmed.

The two are employees of Sage Engineering and were working for Chevron Nigeria when they were abducted during a ship hijack in the Niger Delta on Friday.

An FCO spokeswoman said: "We understand that the company is looking after them. We remain in close contact with the company and remain ready to provide whatever consular assistance is needed."

Kidnappers claim locals do not profit from oil revenue

A spokesman for Chevron in the United States said the governor of the state of Bayelsa had been "instrumental in obtaining their release".

Referring to the earlier releases, the Foreign Office said there were "no details of any injuries" to Mr Welch or Mr Miller, and added that they were being looked after by their employers, Niger-Benue Transport Company (NBTC).

Mr Welch, who is resident in Spain, and Mr Miller, who is understood to be from the Newark area of Nottinghamshire, were seized on Monday outside the company's offices in East Warri.

'Successful conclusion'

Robert Msude, spokesman for NBTC, said their capture was linked to fighting between rival tribes in the region.

Mr Shears, a pilot with Bristow Helicopters, was working under contract to Texaco when he was taken eight days ago.

He was also believed to be uninjured when he was released on Wednesday morning, along with a Nigerian colleague. He has not lived in Britain for several years.

The pilots were kidnapped along with four other Britons when armed kidnappers stormed an oil platform and forced them to fly their helicopter to a nearby village.

The others were released on Friday.

A spokesman for Bristow Helicopters said: "We are delighted, obviously, that this has ended with a successful conclusion to negotiations."

'No benefit from oil'

Kidnapping for ransom has been rising rapidly in Nigerian oil fields in recent years and nine Britons have been captured in the southern Delta region in three separate incidents this month.

Victims are held for ransom by local people who say they get no benefit from the oil.

Those abducted are normally released unharmed within days of being captured.