By Stephen Beech & Zahra Khaliq An ultra rare Aussie coin found in a London charity shop is expected to sell for thousands of pounds at auction next week. The 15p coin, known as a ‘Dump’, dates back to the early 19th century and was found in a bag of coins donated to an Oxfam store in Orpington, south east London. Oxfam volunteer and former banker, John Turner, who first spotted the coin, identified it as a rarity. Mr Turner took the coin to Noonans Mayfair auction house in central London for a second opinion, where experts confirmed that it was an Australian New South Wales 15p piece from 181…