Antiques Roadshow expert, Robert Tilney, was left stunned when he was told that a rare RAF sector clock was bought at an auction for just £20. During tonight’s repeat episode, treasures brought in to be valued include a set of stained-glass windows decorated with mermaids and a piece of costume jewellery found in an antique shop in Australia. Elsewhere, the experts also get their hands on an ornately decorated mandolin found concealed in an old cupboard, a device used to make penicillin, a silver milk jug from Kashmir and a huge bell from a Japanese temple. However, when Tilney came across one…