Chief inspector of prisons Nick Hardwick said the report into Wormwood Scrubs prison was "very disappointing".
He said the prison had found it hard to replace experienced staff who left during a major restructuring last year
Although he said there was "some recent evidence" of action being taken to improve performance, there remains "much to be done".
He emphasised the heavy demands being made on staff, saying: "Many staff appeared extremely stretched and some were clearly frustrated that they could not do more; others appeared to have lost focus on prisoners' needs."
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Police said the child, who was without a driving licence, was trying to make his way 2,500 miles from the east coast to Perth.
The 24-year-old was charged with 14 counts of wounding with intent to do grievous bodily harm and one count of throwing a corrosive fluid.
Winds will veer northerly overnight with colder air streaming in over the next few days.