Sainsbury’s head office was evacuated last night after smoke in a basement room set off the building’s fire alarm.

One eyewitness described seeing ”thick white acrid smoke” coming out of the room in the basement of the Store Support Centre on High Holborn in Central London.

The building was evacuated before security staff informed the fire brigade, which arrived within 10 minutes of the call.

In a statement Sainsbury’s said that the fire started in a cable duct on the pavement of New Fetter Lane, which runs along the side of the building and feeds into the basement, adding that the duct is unrelated to Sainsbury’s. Fire crews found a smouldering cigarette end in the duct, which was clogged up.

A Sainsbury’s spokeswoman said: “A small amount of smoke seeped into the Support Centre basement, setting off the fire alarm at 7pm. The building was reopened just after 8pm with no damage caused and action has been taken to ensure that it doesn’t happen again.”