Recovery workers have been unable to remove the body due to safety fears.
A second body has been found inside a block of flats decimated by fire two weeks ago.
The body has yet to be recovered or identified due to concerns that the building could collapse.
It brings to two the number of confirmed casualties inside the building following the fire on December 15.
A police spokesman said: “Due to the structural instability of the building, it currently remains impossible to recover those who are inside.
“In the weeks since the fire, scaffolding has been put in place around the site and good progress has been made.
“However, in recent days, the building has started to collapse inwards, which has resulted in some parts of the roof falling inside.
“It is, therefore, possible that further collapses will occur due to the instability of the building.
“While it is impossible to predict when or if this will happen, the emergency services continue to monitor the site closely as well as weather conditions which could affect the situation.
“If the collapse does occur, it is expected that this could be loud as well as visible to those living nearby.
“In the event of a collapse, people are advised that they should keep windows and doors closed to prevent dust from entering their homes.”
Hakeem Kigundu, 31, has been charged with murder and arson with intent to endanger life.
He is due before Reading Crown Court in February.