The company hired to fix the roof of Notre-Dame Cathedral before it went up in flames last week has admitted that some of its workers flouted no-smoking regulations on scaffolding around the building. 

The spokesman for Le Bras Frères, Marc Eskenazi, admitted that workers had smoked on the scaffolding because it was "a bit tricky" to get down for a cigarette break, but he denied that this was the cause of the fire, The Telegraph reports.

He said that the smoking was not a factor in how the fire broke out because the scaffolding was far from the point where it started in the roof below the spire.

"There were colleagues who from time to time broke the rules and we regret it," said Mr Eskenazi, who added that they had "admitted to police that they did smoke". 

"In no way did a poorly extinguished cigarette butt start the fire. Anyone who has tried to start a chimney fire knows that not a lot happens when you put a butt on an oak log," he added.

The fire last week damaged large parts of the 850-year-old building, including completely destroying its roof and spire.  Firefighters were able to save the twin bell towers and the main stone structure.

Philippe de Cuverville, finance officer for the Archdiocese of Paris, said that the building "as a whole remains fragile" and "weakened" as a result of the heat and water used to douse the flames.

He said that a detailed analysis of the state of the building would need to take place before they could begin the work of restoration and that it would be several weeks before experts could determine the full impact of the fire on the structure.

"Beyond the audit, the emergency is certainly sealing the building through the setting up of an umbrella, a sort of large protective roof, which could allow us in the medium term, after the restoration of the vault, to re-enter the building for certain religious celebrations. But even that can take years," he said. 

Workers, including mountain climbers, raced against the clock this week to cover the roof in tarpaulins ahead of rain that was forecast for Wednesday. There were fears that rain could further damage the already water-logged building.