The project manager for the architects that refurbished Grenfell Tower has said a firm which made flammable insulation used "deliberately misleading" sales tactics comparable to "masquerading horse meat as beef lasagne".
Neil Crawford, of architects Studio E, told the inquiry into the disaster that Celotex "clearly sought to deceive" and exploit "the understanding that an average architect would have" with the way it presented sales literature for its RS5000 insulation.
The insulation - combined together with Reynobond PE cladding panels - made up the external cladding system, which was found to be a key factor in the fire's rapid spread by acting as a source of fuel.
Referring to Celotex's marketing literature, Mr Crawford told the hearing on Monday: "To be blunt about it, we've obviously seen the recent emails in terms of internal correspondence within Celotex and clearly they sought to deceive based on the understanding an average architect would have with the way they worded this document.
"It's deliberately misleading. It's masquerading horse meat as beef lasagne and people bought it.
"All I can say is the totality of what was written there made me understand that this product was compliant in that use ... it's presenting it as a product suitable for buildings, rainscreen in buildings above 18 metres."
Mr Crawford said he sent the RS5000 product and its literature to fire safety engineers Exova, who gave him a "fairly emphatic confirmation that it was applicable and that it could be used".
He added: "My first port of call was to send it to what I considered a higher fire authority, ie the fire specialist, and asked them to evaluate it. "Exova were fairly emphatic about it being appropriate to use".
Mr Crawford - who is not a registered architect and has asked to be referred to as a project manager - has previously said Studio E was "learning on the job" as it refurbished the high-rise block.
The Celotex RS5000 product was marketed as having "Class 0 performance throughout the entire product", which was the minimum requirement for external surfaces of buildings.
But the inquiry has previously heard Celotex saw Grenfell as a "flagship" for its product and cynically exploited the "smoke of confusion" which surrounded building regulations.
Stephanie Barwise QC, for one group of victims, said it actively promoted RS5000 for use on the 220ft (67m) west London tower block despite knowing it should have been recalled after safety tests.
Celotex has maintained its marketing literature promoted RS5000's use on buildings taller than 18m only on a "rainscreen cladding system with the specific components", used when it passed a fire safety test, and that it stipulated any changes to those components would "need to be considered by the building designer".
"The rainscreen cladding system described in Celotex's marketing literature bore no resemblance to the rainscreen cladding system installed at Grenfell Tower," said its lawyer Craig Orr QC.