The Home Office is not confirming or denying whether any British workers have been involved.
But officials say they are investigating reports which suggest at least one Briton was taken when gunmen stormed a compound belonging to a Lebanese construction company in Nigeria.
ITV News reporter Sejal Karia talks from outside the Foreign Office:
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Four British rowers who became stranded in the Atlantic Ocean after their boat capsized and they lost their oars have been rescued.
The £15 'liquid biopsy' looks for fragments of genetic material in a tiny drop of saliva.
Figures from the latest ComRes poll shows 58 percent believe David Cameron will not get a good deal for Britain.