A subsidiary of Halliburton is under investigation by the UK’s Serious Fraud Office over the US oil service company’s part in an alleged plot to pay more than $170m (£89m) of bribes to win billions of dollars of work at a giant Nigerian gas plant.

The SFO said it had carried out searches at business and residential premises as part of the probe into KBR, whose work on the project was underwritten partly by British government money.