The government still has a "long way to go" to strip all high-rise buildings of dangerous cladding similar to that used on Grenfell Tower, the public spending watchdog has warned.
Three years after the deadly tower block fire, removal work was still outstanding on some 300 buildings, the National Audit Office (NAO) said.
The NAO said work had been particularly slow on private sector buildings.
The government said it had provided £1.6bn for cladding removal.
The flames which rapidly engulfed the 24-storey Grenfell Tower in west London in June 2017 were fuelled by its aluminium composite material (ACM) cladding, an inquiry has previously heard.
Gareth Davies, head of the NAO, said: "The Ministry of Housing, Communities and Local Government (MHCLG) has made progress in overseeing the removal of dangerous cladding from many buildings, particularly in the social housing sector.
"However, the pace of progress has lagged behind its own expectations, particularly in the private residential sector.
"It has a long way to go to make all high-rise buildings safe for residents."
'Covid-19 slowed progress'
Of the 455 buildings over 18m tall identified to be covered in ACM by the MHCLG, 155 have had the cladding removed, 300 are still undergoing work and 160 are still awaiting work, the NAO said.
An NAO report, published on Friday, said "effects of Covid-19, and public health measures taken to limit its impact" had slowed down the speed at which buildings were made safe.
Last week, a parliamentary committee warned fixing all serious fire safety defects in high-risk residential buildings could cost up to £15bn.
In addition to the buildings covered in ACM, another 1,700 are thought to have cladding which could potentially be unsafe.
An MHCLG spokesman said: "We are clear that building owners must keep their residents safe and we are providing them with unprecedented support to do so.
"The Government has provided £1.6bn to ensure unsafe ACM and non-ACM cladding is removed swiftly from high-rise buildings, and is bringing forward the biggest change in building safety in a generation.
"We have made progress with the removal and replacement of ACM cladding, but it is clear there is much more still to be done and building owners have a legal responsibility to ensure their building is safe."