There was no casualties among the British troops that returned to Helmand province for a secret mission, but a number of Afghan soldiers were killed, the Sunday Times said.
During the operation, a number of Taliban insurgents were detained and killed, more than 30 improvised explosive devices were found and destroyed and two vehicles were seized along with ammunition and weapons.
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The suspect, 35-year-old Willie Corey Godbolt, has been arrested and was being treated for a gunshot wound in hospital.
Mohanna Abdhou, known as Montana, was out with friends when two attackers cycled up to them and opened fire in Brent, north-west London.
The US president tweeted that Mrs May gave him "full details" of the incident during talks while he attended summits in Europe.