Get an Oyster Card
Save yourself time, money and the inconvenience of figuring out how much you need to pay while traveling in London by getting an Oyster Card.
At most, you would just have to pay £5.70 per day. With that amount, you can take as many trips as you’d like in central London on trams, buses, tubes and some trains.
Another advantage is that the Oyster Card never expire. If you have leftover credit, you can always just save the card and use it when you return to London or you can just give (sell?) it to another traveler.
A pre-loaded card is worth around US$15. You can get one before you depart for London here.
via Fodor’s.

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