Bus chiefs have launched an investigation after footage emerged which appears to show a driver filming at the wheel.
A video posted on the snap and shame website Scotland’s Worst Drivers apparently recorded by a bus driver shows a tram making a test run along Princes Street.
During the film the camera pans round, revealing the video has been shot from the driver’s cabin of a bus.
The 40-second clip has now been viewed more than 1640 times.
Lothian Buses has pledged to investigate the incident but added it was “impossible to be certain” the vehicle was one of its fleet.
The user who originally uploaded the footage to YouTube has since deleted his YouTube account. It is not known if there were passengers on board at the time.
Drivers of buses could get a maximum fine of £2500 for using a mobile phone at the wheel.
Neil Greig, of the Institute of Advanced Motorists, said: “You expect a high standard from professional drivers. He has let himself and his company down.
“All bus drivers know it’s illegal to be holding a mobile phone for any purpose and the fact he is in charge of a vehicle with other people on it makes it even more shocking.
“I’m sure if he is tracked down he will be disciplined appropriately.”
A spokesman for First Bus said he did not believe the bus was operated by their firm due to the livery and the time of night the footage is understood to have been taken.
Night-time trials in which the trams have run along Princes Street began in December.
Sarah Boyd, head of bus operations at Lothian Buses, said: “Although it’s impossible to be certain that this is one of our buses we will be investigating this incident. If we are able to establish sufficient facts to take action we will do so in line with our normal disciplinary procedures.
“In any case, it is a highly irresponsible act and completely against the stringent training given to our drivers. We will be ensuring the strongest message goes out to our staff about this as safety is our number one priority.”
The city council declined to comment on the footage.
