Thanks, all very helpful.
Another problem. I have now bought an oyster card from a local newsagent. I tried to register the oyster card on my tfl account, trying on the website and the app and both say I need to use the oyster card before I can register it. So to travel using it and then wait 24 hours to register it. Does this mean I have to pay full price travel until the card is registered?
Also, the newsagent charged me £10, when I was expecting £7. Its definitely a standard oyster card, not a visitor one.