Fire service sources say the man, who was dressed in full uniform, claimed to be a senior Strathclyde officer, and first appeared when he turned up at a city station and helped himself to a cup of tea.
Later he joined crews as they tackled the giant blaze that destroyed flats under construction at Hawkhill Close, near to Easter Road Stadium, last month.
He spent at least 15 minutes at the scene of the fire and is said to have discussed tactics with firefighters before being found out and told to leave. Both the police and Lothian and Borders Fire Service said today an investigation was now being carried out and insisted the man was not actually involved in any firefighting operations.
But separate sources told the Evening News that the man took an active part in proceedings when he arrived on the scene of the blaze.
One senior firefighter said: "He tried to engage firefighters in conversations about tactics of firefighting. He tried to engage and prove that he was knowledgeable about firefighting.
"He'd ask things like 'How are you getting on at this point, are you needing any help?', just generally wandering about talking to people."
He said that the man had arrived in a city station, believed to be Tollcross, earlier in the day and helped himself to a cup of tea.
When questioned by staff he said he was a senior figure in the Strathclyde service.
It is not thought he travelled to the fire site with the crew but made his own way there, arriving around two hours into the incident.
It is understood that he was finally discovered when he tried to speak to the senior managers in the command control vehicle.
The Fire Brigade Union in Scotland today hit out at the actions of the man, who it said could have caused harm to himself and members of staff.
Gavin Barrie, regional treasurer of the FBU Scotland, said: "I would hope members of the public would take a responsible attitude.
"Professionally, we have got enough to deal with without people who are imposters appearing at the fire scene potentially putting themselves at great risk and distracting us from our proper task at that time.
"We just have to hope that people are not stupid enough to do it again.
"I've certainly never come across anything like this before.
"In the past, we've had fire engine chasers who use scanners and the rest of it but this is far beyond that.
"To try to appear to be a firefighter is unreal."
A spokeswoman for Lothian and Borders Fire and Rescue Service said: "I can confirm that a man posing as a firefighter presented himself at the scene of the Albion Road incident.
"However, this person was not involved in any firefighting operations and the matter is under investigation."
A police spokeswoman said: "We are looking into the circumstances surrounding the incident and inquiries are ongoing."