Kingspan had threatened the National House Building Council (NHBC) with legal action on the grounds of defamation after the organisation discovered that its K15 insulation product was not compliant with building regulations, the Grenfell Inquiry has been told.

The NHBC, the country’s largest building control body, had warned Kingspan that it would have to start informing projects that had used K15 that it was not compliant. Kingspan responded by instructing lawyers to send a letter in February 2015 to the NHBC saying it would seek a legal injunction under the Defamation Act 2013.