Bowmer & Kirkland was one of several contractors to raise concerns about the fire safety of Kooltherm K15 insulation for use behind cladding for one of its projects back in 2008.

Philip Heath, Kingspan Insulation technical manager, said builders asking questions were mistaking him for ‘someone who gives a damn’.

He added in the email forwarded to a friend: “I’m trying to think of a way out of this one, imagine a fire running up this tower!!!!!!!! Any ideas. P.S. I don’t do technical on Fridays.”

Bowmer and Kirkland then forwarded the query to facade engineering consultant Wintech.

It advised Bowmer and Kirkland that Kingspan insulation would not be appropriate.

“Kingspan keep repeating that the product… is suitable for use in buildings over 18m. What they fail to say is that it is suitable only in the configuration tested,” wrote Wintech.

To an employee warning Heath there could be legal issues after Wintech raised its fire safety concerns, he replied: “Wintech can go f’#ck themselves, and if they are not careful we’ll sue the a’#se [ off ] them.”

Under cross-examination by counsel to the inquiry, Kate Grange QC, asked: “Can you explain why you wrote that, given that Wintech were giving entirely accurate advice to their customers?”

Heath admitted to the Inquiry “It was totally unprofessional… I think it was just frustration that we were going round in circles with them.”

During his evidence it also emerged that Kingspan did not consider withdrawing an insulation product from the high-rise market despite it failing a fire test, the inquiry into the disaster has heard.

Instead the inquiry heard Kingspan changed the make-up of its Kooltherm K15 insulation after 2005 without amending the marketing material stating it was suitable for use on buildings over 18 metres and had passed a relevant fire test.

Heath, who still works at Kingspan now as a divisional development director, agreed that there was no valid test evidence throughout 2006 to 2010 based on which K15 then being sold could comply with building regulations for use over 18m.

Kooltherm K15 was one of two types of insulation used that turned out to be combustible on the Grenfell building, although they were widely seen as being of limited combustibility.