A Suffolk firm was “dishonest” by “over-engineering” a cladding fire safety test to achieve a pass for its insulation product, a former worker has told the inquiry into the Grenfell Tower tragedy.

Jonathan Roper, former assistant product manager at Celotex - manufacturers of flammable insulation and the Rs5000 product used on the London tower - admitted complying with acts which were “completely unethical” and a “fraud on the market” during the public hearing into the June 2017 tragedy, in which 72 people died.

MORE: Suffolk firm was misleading over insulation, sales manager tells Grenfell inquiryA first fire test failed in January 2014, but a second system passed in 2014.

Celotex, whch is based in Lady Lane, Hadleigh, used this to erroneously market the combustible rigid foam boards as being safe for use on high-rise buildings, the inquiry has heard.

In latest evidence, the inquiry heard Celotex added a 6mm fire-resisting magnesium oxide board to a cladding test rig made up of 12mm fibre cement panels for the second test.

The inquiry heard 8mm fibre cement panels were added over the magnesium oxide to “conceal” its presence, making the whole system almost flush - but for the 2mm difference.

Mr Roper agreed with the inquiry’s chief lawyer Richard Millett QC that the decision to use “a thinner layer was to make it less noticeable there was something else behind it”.

That would aid to “see off any prospect of anyone asking questions” about its make-up.

Asked whether he felt that was “dishonest”, Mr Roper agreed and said he “felt incredibly uncomfortable with it”.

However, he told the inquiry there was no-one in the firm he could tell about his concerns.

“I went along with a lot of actions at Celotex that, looking back on reflection, were completely unethical and that I probably didn’t potentially consider the impact of at the time,” said Mr Roper.

“I was 22 or 23, first job, I thought this was standard practice albeit it did sit very uncomfortably with me.”

Mr Roper has told the inquiry that all his work was overseen by product manager Paul Evans, and that the motivation for getting the Rs5000 product to market was to compete with rival firm Kingspan and its K15 insulation.

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 at the time.

Celotex, part of the French multinational Saint-Gobain group, has maintained it promoted Rs5000’s use on buildings taller than 18m only on a “rainscreen cladding system with the specific components”, used when it passed the fire safety test.

In its opening statement for module two of the inquiry, the firm said: “In the course of investigations carried out by Celotex after the Grenfell Tower fire, certain issues emerged concerning the testing, certification and marketing of Celotex’s products ... These matters involved unacceptable conduct on the part of a number of employees.”

The proceedings continue.