Showers at top security Belmarsh prison housing killer Axel Rudakubana were found to be unhygienic during an inspection.
A report said the main segregation unit and segregation cells in the high security unit were dirty and the showers unsanitary.
It was one of 14 priority concerns raised by inspectors.
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They also found many cells were poorly equipped and lacked basic necessities such as bedding, clothing and chairs.
Other concerns included poorly maintained outdoor areas which had deteriorated since a last inspection, as reported by Need To Know.
The report said the potentially attractive grounds were not well kept and contained a large amount of litter.
An action was plan drawn up in response to the findings.
It said a full living conditions review would be carried out.
The showers are set to be revamped.
An update to the action plan revealed some progress addressing the priority concerns had been made.
The report the issue was a ‘concern’ and reads: “The main segregation unit and segregation cells in the high security unit were dirty and the showers unsanitary.
“Many cells were poorly equipped and lacked basic necessities such as bedding, clothing and chairs.”
In terms of action taken, it adds: “A full living conditions review of the Main Segregation Unit and Segregation Unit within the High Security Unit will be conducted.
“And systems put in place to ensure cleanliness, mandatory equipment and basic necessities meet desired standards.
“A capital bid to refurbish the showers in both areas will be submitted.”
Rudakubana is serving life in jail for murdering Alice da Silva Aguiar, nine, Bebe King, six, and Elsie Dot Stancombe, seven, at a Taylor Swift-themed dance class in Southport last July.
Earlier this month it was reported police were investigating an alleged attack by him on a prison officer.
He was in his cell at Belmarsh at the time and allegedly heated water up using a kettle in the room, its alleged.
He then threw the boiling water at the officer, who was standing outside the cell, through a hatch in his door, it was claimed.
The member of prison staff was taken to hospital as a precaution but only suffered minor injuries.
Other infamous Belmarsh inmates include Grindr killer Stephen Port and Ali Harbi Ali who murdered MP David Amess.
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