A newly-discovered early watercolour by JMW Turner is expected to fetch at least £20,000-£30,000 at the Cheffins Fine Sale in Cambridge on 20-21 March. Depicting the Entrance to Bishop Vaughan’s Chapel in St David’s, Wales, it is signed ‘W Turner’ and can be dated to the artist’s 1795 tour of Wales. It has been held in a private Suffolk collection for the past 30 years, having being bought in a group lot of paintings for about £100. The anonymous owner thought it might have been a Turner, and contacted Cheffins, which sold a previously untraced Turner watercolour of Chepstow Castle from a simi…