Can anyone who knows about England traffic laws tell me why this cop was wrong...scenario follows...?

Driver approaching small painted on roundabout on a quiet road indicates and cuts the roundabout to go right, seeing there is nothing coming from the right and then pulls in when they see a police car with siren on, which was at the left of the roundabout, approaching from behind... to let it pass. Police car going... show more Driver approaching small painted on roundabout on a quiet road indicates and cuts the roundabout to go right, seeing there is nothing coming from the right and then pulls in when they see a police car with siren on, which was at the left of the roundabout, approaching from behind... to let it pass.
Police car going to an emergency stops by the driver for almost a minute, saying You don't cut a roundabout do you, and you give way!
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