Warnings that insulation used on the Grenfell Tower should only be used with non-combustible cladding were in place from as far back as 2014, the latest reports suggest.

The Guardian has reported viewing a formal certificate issued by building inspector organisation the Local Authority Building Control which it said stated that the synthetic insulation chosen for a £10m refurbishment of the tower was acceptable for use on tall buildings only if used with non-flammable fibre cement panels but were used in Grenfell’s case with combustible polyethylene panels.

The publication says photographs of the build provide a clear view of the materials being used for the cladding.

According to the report, the insulation known as Celotex RS5000, was made from polyisocyanurate – which burns when exposed to heat and gives off toxic cyanide fumes.

In addition, the manufacturer of the insulation had specified that the fire performance report pertaining to the material related to the specific components which had been used in the test – any changes to which (or changes to construction methods used) would need to be considered by the building designer.

In addition, the web site reported that a second combustible insulation material from insulation provider Kingspan was used, but as part of a combination for which the manufacturer says it would never have recommended, had never been tested with polyethylene core aluminium panels and would be surprised if some a system would pass the British Standard 8414 large-scale test.

The latest reports raise further questions about why the building control team of the Royal Borough of Kensington and Chelsea certified the work – in respect of which council building inspectors had conducted sixteen site visits over a two-year period ending July 2016.

Since the fire, both the Celotex insulation and the Reynobond PE aluminium cladding have been withdrawn from sale – both of which were less expensive compared with non-combustible alternatives.

Current estimates from police put the death toll of the Grenfell fires at around 80.

Police are investigating possible charges for manslaughter as well as any other breaches of legislation and regulations.