In the Phase 1 report of the Grenfell Tower inquiry Sir Martin Moore-Bick has expressed his conclusion on the compliance of the tower's external faade with the Building Regulations. Sir Martin accepted that the construction of the Regulations is ultimately a question of law and said there is compelling evidence that requirement B4(1) was not met in this case. Although, in another context, there might be room for argument about the precise scope of the word "adequately", the functional requirements of the Regulations inevitably contemplate that the exterior must resist the spread of fire to some significant degree appropriate to the height, use and position of the building.
He also accepted that the cladding of the external walls constituted "building work" within the meaning of regulation 3 of the Regulations, because it involved a "material alteration" of the building which resulted in its ceasing to comply with requirement B4(1). In particular, before the fire, the exterior walls of the building, constructed of concrete, complied fully with that requirement, since concrete does not support combustion, but that changed fundamentally when the cladding system was added during the main refurbishment.
A separate question for investigation in Phase 2 was how those responsible for the design and construction of the cladding system and the work associated with it, such as the replacement of the windows and infill panels, satisfied themselves that on completion of the work the building would meet requirement B4(1).
See, at page 583 in volume 4 of the full report: https://assets.grenfelltowerinquiry.org.uk/GTI - Phase 1 full report - volume 4.pdf