Video: Prince Charles and the Duchess of Cornwall take the tube Joining the hoi polloi the heir to the throne used his oyster card to swipe his way through the barriers at Farringdon station and took the Metropolitan line, where he managed to get a seat, to King's Cross. They made the visit to mark the 150th anniversary of the capital's transport network. Although they both qualify for a Freedom Pass for the over-60s, they were presented with special limited edition commemorative oyster cards by staff which had £10 credit on for the journey, which costs £2.10. When they reached Kings Cross the Duchess took the opportunity to visit "Platform 9 3/4" where the Hogwarts Express leaves from in the Harry Potter books.