Police said both the insulation and tiles used in cladding at the 24-storey Grenfell Tower block failed all post-fire safety tests.
"Preliminary tests show the insulation samples collected from Grenfell tower combusted soon after the test started," McCormack said.
Such were their concerns after the tests that the information was immediately shared with government to disseminate more widely.
"Given the deaths of so many people we are considering manslaughter as well as criminal offences and breaches of legislation and regulations," McCormack said.
The blaze, Britain's worst since World War Two, has heaped pressure on Prime Minister Theresa May, already fighting for her political survival after her party lost its parliamentary majority in a snap election on June 8.
When speaking about the 79 people dead, presumed dead or missing, McCormack said: "I fear that there are more."