A strict Government interpretation of building regulations has been blamed for scores of high-rise towers failing fire tests.
An expert has alleged the current round of safety assessments pose a "massive inconsistency" with industry standards, which are vague on whether cladding should be non-combustible.
Flammable cladding has been found on 75 tower blocks across 26 local authority areas, leading to calls for councils to urgently send samples for assessment.
The so-called combustibility test, carried out by the Building Research Establishment, has been failed by every building examined so far, Communities and Local Government Secretary Sajid Javid said on Monday.
But David Metcalfe, head of the Centre for Window and Cladding Technology, a body which works with hundreds of contractors, architects and manufacturers, claimed samples were being tested "severely".
He added that the apparent scale of the building safety crisis risked being inflated by the cladding being scrutinised in isolation, rather than as part of a whole design system which could be safe.
The exact nature of the Government-backed tests has not been made public, but Mr Javid confirmed samples were being ranked on a scale of one to three - with those in categories two and three considered a failure.
Mr Metcalfe told the Press Association: "All these products are failing, which I don't think is any great surprise; the bigger issue is that it is not entirely clear whether or not the products, in accordance with the regulations, have to be of limited combustibility in the first place.
"In terms of combustibility, the regulations refer to insulation products and filler materials. I don't know what a filler material is, that is not defined anywhere in the regulation, so the regulations don't say specifically the cladding should be of limited combustibility.
"Timber isn't an insulation product, it's not a filler material, so there's nothing stopping you using timber on a high-rise building, but the Government now are saying that all cladding should be of limited combustibility - there is a massive inconsistency there.
"With the Government's new strict interpretation of the rules, we can say these products do not meet the prescriptive requirements. We have this approved document which gives you some simple rules you could follow, and if you follow these rules you are deemed to have complied with the regulations; it's that document which is unclear.
"They are interpreting that document to say the cladding should have been of limited combustibility but it doesn't actually say that; they are testing it more severely than might have been done in the past because people didn't think it required that level of testing."
His analysis follows claims on Monday by Housing Minister Alok Sharma that building regulations were "very clear" that that type of cladding was "non-compliant" on buildings over 18 metres (59ft).
Many councils have responded to news that their buildings' cladding failed fire tests by saying the non-combustible material used in the insulation mitigates the risk of flames spreading.
Asked if this meant the risk to public safety appeared greater than it was due to the failed tests, Mr Metcalfe said: "I'm not saying it's easy, they are in a very, very difficult position, they have to be seen to be doing something. What they are doing is probably about right - but it doesn't necessarily reflect what is going to happen on a building.
"You are testing a material in isolation; what we need to consider is how it performs as a system - it's the cladding, it's the support system, it's the insulation, it's the cavity barriers, it's all of these things combined to determines what happens in a fire."
The number of fires in high-rise purpose-built flats fell by almost half in the years leading up to the Grenfell Tower disaster, new figures from the Home Office showed on Tuesday.
Fears have also been expressed that contractors might have been confused by cladding with a category zero rating - meaning it has high fire resistance but is still flammable - mistakenly thinking this meant it was non-combustible.
Hospitals and schools are being tested to make sure they are not encased in combustible cladding, and Mr Javid said 15 buildings "across the wider government estate" require further investigation.
Mr Javid admitted multiple fire safety inspection failures had been discovered in tower blocks which were evacuated last week in Camden, north London.
He said "literally hundreds of fire doors were missing" from high-rises there, as he outlined other failures including inaccessible stairways and breaches of internal walls.
"The fact that all samples so far have failed underlines the value of the testing programme and the vital importance of submitting samples urgently," he told the Commons.
One Grenfell residents' group, part of the Justice4Grenfell campaign, welcomed the public inquiry but warned that the voices of locals must be heard.
In an open letter to Prime Minister Theresa May and Home Secretary Amber Rudd, it demanded immediate funding for legal advice for bereaved families and survivors.
It added: "The investigation must leave no stone unturned. It must identify each and every individual and organisation who must bear responsibility and accountability for this tragedy and the mishandling of the aftermath."