Martin Westbury and his son Benjamin, two, were set free early yesterday after spending the night as hostages in the Nigel delta area of the country.
Mr Westbury's sister, of Rossendale, Lancashire, who asked not to be named, said the whole family were greatly relieved. She said: "All we know is we were called at 6.30 this morning and informed that they were safe and well."
She said she and her parents, who also live in Lancashire, had spoken briefly to Mr Westbury. He moved out to Nigeria last year with his wife, Lindsay. He had reassured them he was safe but tired. "We are hoping to have a proper chat with him when they have had a long rest. It was just so good to hear his voice."
Mr Westbury, 39, who works for the oil company Shell International as head teacher of the Shell school in Warri, was thought to have been abducted by local youths.
A spokesman for Shell in Nigeria said the pair were bundled into a speedboat at gunpoint on Sunday as they cycled in Ogunu, near Warri. He confirmed that they were returned to the Shell compound in Warri early yesterday. The spokes-man said: "The local chiefs organised a search party and found them, then they were kind enough to bring them home. I believe they have been to a clinic for a check-up and are now back at home resting. They are very tired by the experience, but they are not hurt."
The primary school caters for the children of expatriate workers and staff in the Warri area.
The spokesman added: "We will be interested to find out more details...so that we can make sure we can function better and protect...our staff."
A spokeswoman for Shell in London said no ransom had been paid. "There were never any demands made."Reuse content