The document contained important requirements regarding the fire hazards of certain cladding materials and was required to be kept on-site under National Building Specifications (NBS), the hearing was told in London on Thursday.

But Simon Lawrence, the contracts manager at main contractor Rydon, told the inquiry it was "reliant on others" and said its sub-contracted design team including architects Studio E and external wall firm Harley Facades bore responsibility for making sure any materials used were safe and compliant.

The inquiry heard the NBS required a copy be kept on-site of the Standard for Systemised Building Envelopes compiled by the Centre for Window and Cladding Technology (CWCT).

The document states: "The building envelope shall not be composed of materials which readily support combustion, add significantly to the fire load, and/or give off toxic fumes."

The inquiry has already found that the plastic-filled Reynobond aluminium composite material panels and combustible Celotex Rs5000 insulation used on Grenfell Tower's cladding system fuelled the fire's rapid spread through the 24-storey block in June 2017, killing 72 people.

Asked about the guidance by inquiry lawyer Richard Millett QC, Lawrence said: "We wouldn't have had a copy on site. It obviously wasn't picked up in all the documents we had to go through ... it obviously wasn't noticed."

Lawrence said the "sheer amount of information" led to it being missed, but said he was familiar with the "principle" of the guidance but not the "technical part".

He added: "You wouldn't assume to be building a, dare I say it, a building that's unsafe."

Asked about Rydon's processes to supervise the overall project and make sure the works were being completed with safe materials, he said: "I think it would be using a competent design team, competent specialist contractors, backed up by building control and all the layers within."

He agreed this boiled down to "reliance on others", adding: "I would imagine specialist cladding contractors were also CWCT members so I would expect them to understand this document."

Lawrence, who was involved in the Grenfell revamp between June 2014 and October 2015, said in his witness statement: "The contractual expectations required the subcontractors to produce a design or specify the use of a material that was both compliant with legal standards and suitable for the project.

"I would expect a contractor to flag up an issue, if they believed that there was a problem with compliance or suitability."

His statement added that "at no point" did he "have any reason to believe" materials were to be used which did not meet legal requirements.

Referring to his statement, Millett asked: "Although Rydon had undertaken express contractual obligations to the TMO (tenant management organisation), your understanding at the time was that you complied with those obligations by farming it all out to others?"

Lawrence replied "Correct", adding: "We would use, obviously, contracts and delegated responsibilities so others complied and were contractually obliged to comply the same as we were."

Australian Associated Press