The main contractor behind the restoration of Glasgow School of Art was condemned for previous fire safety failings, it has emerged, as bosses insisted heat and smoke detectors – as well as guards – had been installed at the Mackintosh building prior to the devastating blaze.

Kier Construction hit the headlines last month for its “criminal” work on the DG One leisure centre in Dumfries – with an inquiry ruling there had been “extensive failures” in its fire safety measures.

Last night, the firm insisted it had implemented a fire safety strategy during the project to rebuild the Mackintosh building following 2014's blaze, which included regular evacuation tests and 24/7 security and fire patrols by a team of three guards.

READ MORE: Roger Billcliffe: Were lessons learned from 2014 Mackintosh fire?

But when asked whether these precautions had been operational on the night of Friday’s blaze, a spokeswoman refused to comment further.

There is no suggestion Kier Construction was responsible for the fire that left the Glasgow School of Art a burnt-out shell.

It comes as fire chiefs confirmed they will examine safety measures as part of a major investigation, while council officials offered a glimmer of hope that the building could be saved.

Assistant Chief Officer David McGowan said the multi-agency investigation will take a "significant period of time", but vowed: "We will uncover the facts."

READ MORE: Lessons for a possible Glasgow School of Art restoration can be learned from Germany, Latvia - and Raasay

Flames tore through the celebrated Mackintosh building after it caught fire at about 11.20pm on Friday, with the blaze rapidly spreading to nearby buildings including the O2 ABC music venue.

It is understood the fire started in the structure’s east wing. Sources suggest it may be up to six months before investigators can say officially what caused the disaster.

But Glasgow City Council said a consensus was emerging that the majority of the building's external fabric would be "saveable", except for the eastern gable. It said those involved were operating on the understanding the structure would be saved.

Last night, details emerged of the difficulties encountered by firefighters as they desperately fought to control the flames.

READ MORE: Roger Billcliffe: Were lessons learned from 2014 Mackintosh fire?

Two engines had to be replaced after suffering “mechanical defects” in the extreme conditions, while crews also wrestled with water supply challenges.

At its height, 120 firefighters battled the blaze from the ground, with 24 fire engines and 11 specialist vehicles at the scene.

Experts fear rebuilding the heavily damaged masterpiece, designed by Charles Rennie Mackintosh at the end of the 19th century, could cost well over £100 million. Some insist demolition may be necessary.

Kier Construction was heavily criticised for its work on DG One leisure centre, which opened in May 2008 at a cost of £17 million but was forced to close just six years later after a catalogue of construction defects were discovered.

READ MORE: Lessons for a possible Glasgow School of Art restoration can be learned from Germany, Latvia - and Raasay

An inquiry report, which was released last month, condemned the “virtually unprecedented” number of faults permeating nearly all aspects of the building.

Professor John Cole, who led the probe, wrote: “This Inquiry would particularly wish to bring attention to the extensive failures in regard to the omissions and inadequate installation of fire-stopping discovered throughout the DG One building.

“The scale of these omissions served to completely compromise the fire safety strategy for the building.”

READ MORE: Roger Billcliffe: Were lessons learned from 2014 Mackintosh fire?

Mr Cole said Kier Northern – now Kier Construction Scotland and North East – was “unquestionably” responsible for the shoddy work identified in DG One, which was later branded “criminal” by an MSP in Holyrood. Taxpayers are set to dish out more money repairing the centre than it cost to build.

Kier has been behind a number of other projects across Scotland, and was recently lined up for a series of lucrative contracts revamping Faslane naval base.

Keith MacGillivray, chief executive of the British Automatic Fire Sprinkler Association, said a sprinkler system was in the process of being installed in the Mackintosh building but had not yet been completed.

He said installing a temporary system, which could have helped control the flames, would have cost a fraction of the £35 million renovation costs.

READ MORE: Lessons for a possible Glasgow School of Art restoration can be learned from Germany, Latvia - and Raasay

Referring to similar issues before the 2014 blaze, he said: “What I don’t understand is they would have carried out a full fire risk assessment after the last fire, and I’m surprised that a temporary system was not recommended.”

Meanwhile, Chris McGlone of the Fire Brigades Union suggested the damage to the A-listed building was so extensive that investigators may never discover the cause of the fire.

Scottish ministers met with leaders at the Glasgow School of Art yesterday afternoon, with a “multi-agency group” of conservation experts established to advise on the way forward.

Culture Secretary Fiona Hyslop insisted: “No-one can fail to have been moved by the images of the fire and its aftermath”.

READ MORE: Roger Billcliffe: Were lessons learned from 2014 Mackintosh fire?

In Westminster, Commons Speaker John Bercow spoke of his "real misery" on hearing of the "terrible tragedy".

A Kier spokeswoman said: “An agreed fire safety strategy was implemented for the build phase of the Mackintosh restoration project, which combined measures for the protection of all those entering the site to work and to alert the authorities in the event of an outbreak of fire.

“These included a smoke and heat detection system and regular evacuation tests as well as 24 hour, 7 days a week security and fire warden patrols by a team of three guards, originally appointed by the client after the 2014 fire and subsequently by Kier.

“We continue to work with and support Scottish Fire and Rescue Service and our client as they determine the next steps for the Mackintosh building and site.

“We have a passionate team of local construction and crafts people, skilled conservators, supply chain and engineering specialists who have worked incredibly hard on this iconic landmark, and together we are all keen to do whatever we can to help moving forward.”