A fire was started at HMP Ranby during an ongoing disturbance which saw 120 inmates refused to return to their cells, The Prison Officers' Association (POA) said.
A spokesman for the Prison Service said minor damage was sustained and there were no injuries to staff or prisoners.
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Turning wet and windy from the west overnight.
The former shadow business secretary Clive Lewis made the comments at an event backed by Momentum.
Look up to the sky this weekend, and you might catch sight of one of the greatest natural spectacles of the year: The Orionid meteor shower.