The sentencing hearing for a gang of underworld gun suppliers had to be abandoned after a newly rebuilt court building was unable to cope with the hot temperatures.
The sentencing at Harrow Crown Court in North London on Friday was for five men and a woman who pleaded guilty to conspiracy to supply firearms and related charges.
It was to include Faisal Razzaq, 44, one of two getaway drivers in the killing of PC Sharon Beshenivsky in Bradford in November 2005.
Razzaq - who was jailed for manslaughter until 2017 - has spent nearly two years awaiting sentencing after pleading guilty to the supply of reactivated blank-firing handguns.
However, staff could not keep the courtroom temperature below 26C during the heatwave, which could bring highs of 38C.
Health and safety regulations meant the Serco dock officers were not allowed to work in temperatures exceeding 26C and that the mobile air conditioning unit could not be moved into the dock.
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Razzaq's barrister, Joe Hingston, asked for the hearing to go ahead with fewer defendants in the dock, but the judge, Hannah Kinch, said: "We have done everything we can to find a way through to allow the hearing to take place today but we have not been able to do so.
"I understand the frustration, but my overriding concern is that this is a fair hearing and that cannot take place today."
The hearing was delayed by more than an hour as the staff attempted to lower the temperature, but the judge said it was likely to rise again when all the defendants and security officers were in the dock.
"This hearing has to be conducted in a sensible manner, which in my view does not involve rising every 10 minutes. I don't see how we can have a coherent hearing," she said.
A new date was set for the hearing in October.
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Harrow Crown Court reopened in April after a three-year £26m renovation caused by the discovery of reinforced autoclaved aerated concrete (RAAC).
The building, completed in 1991, has built-in air conditioning, but two mobile units had to be brought into court one in the building in an attempt to lower the temperature, which is not permitted under regulations.
It comes after a justice minister said there were more than 80,061 outstanding cases in the crown courts at the end of March, which will take around 300 years to clear at current rates of progress.
(c) Sky News 2026: London court abandons sentencing due to heatwave temperatures
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