A tram driver has been suspended after footage in The Sun appeared to show him falling asleep, transport company FirstGroup has said.
The footage suggested he may have nodded off at the controls on the same line in which a crash killed seven people in Croydon on 9 November.
The Sun said it was recorded in April, about three miles from the south London derailment which also injured 51.
FirstGroup said the driver was removed from duty pending an investigation.
A spokesman for the company said: “We have not seen this video before (we saw the footage for the first time when the Sun sent it last night) and it will now be subject to a full investigation.
“If the situation is as it appears, then this is completely unacceptable and appropriate action will be taken.”
In a 30-second clip the driver – who is not the same one involved in last week’s fatal crash – appears to drift in and out of sleep as the tram moves forward.
He is seen apparently struggling to remain upright as passengers are heard expressing shock as the tram approaches the next stop.
Mayor of London Sadiq Khan said he was “extremely concerned” by the footage.
The BBC has not been able to verify the footage, but Transport for London said it was also carrying out urgent inquiries.
A spokesman said it had asked operators FirstGroup to take all necessary action and report back as soon as possible.