A couple from Beverley have scooped £2.2 million on the National Lottery.
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Gates giving access to the walls have been shut between Fishergate Bar and Postern Tower.
Olivia Bonnick-Campbell is thought to be carrying a black handbag and wearing a silver necklace with large, hooped earrings.
The gallery is the only British museum on the list of 46 nominees from 24 countries.