Update (Oct 2023) - it looks like travelcards are not being scrapped.
When purchasing tickets for the day, you will need to ensure that your travelcard covers zones 1 &2
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The withdrawal of Travelcards is hugely frustrating, and certainly makes things a bit more complex in terms of organisation.
At the current time, we believe that you should still be able to get a travelcard as part of a National Rail ticket if you're arriving by train, the other option is to use Oyster cards, or contactless payment cards. You can purchase Oyster cards in advance through TfL's website (https://visitorshop.tfl.gov.uk/en/london-visitor-oyster-card) They're £5 each for the card itself but don't expire, so you'd be able to use them for any trips to London in the future. Once you've bought the card, you simply load it with the amount of credit that you require (currently £6.70 for 1 day travel in central London).
We will updated our socials and FAQ's once we know more about what the withdrawal looks like. Apologies for the inconvenience this causes, but unfortunately it's out of our hands!