According to The Observer, citing a leaked copy of the inquiry's report, the government account of the attack will describe it as a "simple and inexpensive" plot hatched by four British bombers bent on martyrdom.
The report also rejects earlier theories that an al-Qaeda fixer, presumed to be from Pakistan, was instrumental in planning the bombings, the paper reported on Sunday.
And it discounts the existence of a possible fifth bomber - a possibility raised by the discovery of a backpack full of explosives in a car used by the bombers.
The attacks on July 7, 2005, left 56 people dead, including the four bombers.
According to the paper, the report says the four men found all the information they needed by scouring terrorism-related sites on the internet.
Their backpack bombs, it says, cost only a few hundred dollars to make.
"The London attacks were a modest, simple affair by four seemingly normal men using the internet," the paper quotes a government source as saying.
Although the inquiry discounts any evidence of overseas links or support to the four bombers - Siddique Khan, Hasib Hussain, Shehzad Tanweer and Jermaine Lindsay - it does note that they were partly inspired by Khan's trips to Pakistan.
"The London attacks were a modest, simple affair by four seemingly normal men using the internet"
Unnamed UK government source, speaking to The Observer
According to the report, meetings between the four men and known "militants" in Pakistan were ideological, rather than fact-finding.
Meanwhile a report into the attack by the Commons intelligence and security committee, which could be published alongside the official narrative, will question why intelligence officials called off surveillance of Khan before the July 7 bombings, The Observer said in its report.
Khan, confirmed as the ringleader of the attacks, was identified by intelligence officers several months before the attacks, the Observer reports.
Opposition politicians have said the leaked details of the inquiry will raise many more questions.
The report, for example, does not shed any light on how the four men came to meet. It also raises concerns over the continued security threat posed by small, independent, unsophisticated groups.
Reduced terror alert
Patrick Mercer, shadow homeland security spokesman for the opposition Conservative party, told The Observer that "a series of reports such as this narrative simply does not answer questions such as the reduced terror alert before the attack, the apparent involvement of al-Qaeda and links to earlier or later terrorist plots."
If confirmed, he said, the official findings would only lead to calls for a full independent inquiry into the issues surrounding the attacks.
The full report of the government inquiry into the bombings is due to be published in the next few weeks, the paper said.