Bailey particularly blamed Class O materials, which are rated for restricting surface spread of fire but can contain highly flammable elements for creating widespread confusion about product performance in the industry.

Bailey, who spent two days being questioned intensively about his firm’s involvement in the project, blamed confusing and sometimes misleading manufacturer claims, convoluted testing regimes and complicated regulations for widespread confusion about good practice in construction.

During his evidence, it emerged that Celotex RS5000 insulation and Kingspan Kooltherm K15 insulation fitted by Harley for the Grenfell refurbishment should never have been used.

These were described as “Class O” by its manufacturers but were not rated as being of “limited combustibility”.

It also emerged that styrofoam and Kingspan TP10 rigid insulation usually sold for roofing insulation, used in the core of the sandwich panels around windows was not compliant.

Asked whether he would change anything Bailey said: “Looking back to what we knew then, certification that we had, the industry practices that were used throughout the UK, if we were faced with the same job now, I suspect, I’m pretty certain, that we would have done it exactly as we did back then.

“I can’t think for a second that anybody in the construction team working on Grenfell or on the hundreds of other buildings that we similarly constructed across the UK, nobody would have thought for one minute that anything we were doing was unsafe.

“But if I could go back in time, armed with what I know now, the certification, the testing regimes, the caveats, the misinterpretation of the Building Regulations, that are not just restricted to us but the whole industry, this stuff, Reynobond, Celotex, Kingspan, none of it would be on the wall.”

He said: “The legislation is complicated to use, it’s not very clear, and I think any form of combustible insulation or cladding should be banned immediately.

“I know that’s not my place to say, but if the building regs banned it, it wouldn’t be on the building.

“Class 0, as I sort of understand how that came into being, was some industry self – interest body created this false class and it’s clouded everybody’s judgement and belief over the past 40 years.”