Michael Perkins, 49, a road policing officer based at Chichester, appeared at Hastings Magistrates' Court charged with common assault and a public order offence.
He was found guilty of common assault against a woman prisoner he was transporting to custody in November 2011 after she had been arrested on suspicion of drink driving. He was fined £495 and ordered to pay £900 costs. He was found not guilty on a charge of using threatening words or behaviour.
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Thursday morning's weather for the east of the region
Thursday morning's weather for the west of the region
Prisons will be expected to reform prisoners as well as punish them under new proposals, set to be unveiled on Thursday.