A British Airways flight bound for Switzerland was forced to return to Heathrow after a suspected technical fault.
Flight BA752 departed from London at 7.47am on Wednesday en route to Basel but was forced to turn back less than an hour later following a problem.
Pictures taken at the airport show fire engines around the A320 plane after reports smoke had filled the cabin.
But British Airways dismissed the speculation, adding the fire engines were sent as a precaution.
London Fire Brigade confirmed it was sent to the airport at around 8.40am but the incident was stood down 10 minutes later.
A British Airways spokeswoman said the airline had apologised to passengers and that another plane had taken the passengers to Switzerland.
She said: “The safety of our customers and crew is always our top priority, and our flight returned to the airport due to a suspected technical fault with the aircraft.
"Our customers are already on their way to Basel on an alternative aircraft.
"The presence of the fire services was purely a precautionary measure."
