We (USA) have requested and just received contactless versions of our Capital One Visa cards. There have been stories of US Visa contactless cards not working in London. We arrive at Gatwick in September and wondered if there is any way to test our cards before we try to board a Thameslink train, or do we just try to use them and if they don't work we'll have to go back and get Oysters. How far would that be? Thanks.