I have looked everywhere but can find no definitive answers to this question. We are in London for less than 24 hours. We need transportation to central London, around London, then back to Heathrow. There are 3 of us. Using a contactless card option to pay as we go isn't a great option as we generally use the same card and I'm not sure if we'll have mobile data to use Apple Pay. I'd rather have a ticket in hand. Buying an Oyster Card sounds like a waste of money as you don't get it refunded until 6 months later. Buying single fares, even if we did contactless, will be more expensive than the 15 pound One Day London TravelCard.
I know you can purchase the ONE DAY London TravelCard online. BUT, can you also purchase it in person at T5 in Heathrow?
I'd rather purchase later just in case -- and not risk not needing it due to plane changes, etc.