At the Old Bailey earlier, as the deluge increased, Judge Anuja Dhir had to abandon the hearing and evacuate the jury from court.
Proceedings were halted and jurors ran for cover when water started dripping on to the heads of the panel hearing the prosecution case.
Staff then tried to catch the cascade in water jugs and waste paper bins and mop up pools of water in the jury box and press area.
Bin liners were draped over the historic woodwork to try to prevent the sodden timbers rotting.
'It started leaking on to the jury and we had to stop the trial,' said a member of staff. The case will have to carry on in a different court.'
Senior judges and maintenance staff have been inspecting the damage this afternoon.
The oak-panelled Number Three court adjoins the Grand Hall of the Old Bailey and is part of most historic area of the famous court building, which was completed in 1907 on the site of Newgate Prison.
Jurors were trying the case of Stanislavs Leonovs who is accused of attempting to murder a rival in a gangland shooting.