Does anyone know if Android Pay would work with TFL in London?

Unlikely. I recommend getting a tourist Oyster card (before you go, but I understand you can get them on arrival). Absent phone/app (and convenient balance tracking), it's still an enormously useful part of navigating London.

Set it up last week and didn't expect to use it much -- if at all. Found myself at the grocery store today only to realize I'd accidentally left my wallet at home. Voila! Android Pay. I'm glad it even occurred to me, because I wasn't excited about going home to retrieve my wallet and return to the store.

I'd sooner just use a contactless credit card that I have instead of dealing with the purchase/setup of an Oyster card.

Any reason Android Pay would be different than Apple Pay (which is supported)?

Mainly because Google has been very slow in launching outside of the US. I expect it will work eventually. Personally, I don't like contactless debit/credit cards, but the fingerprint security that comes with Apple (and presumably Android) pay is appealing.

That said..... There's no harm in trying. As far as the payment terminal is concerned, there may not be much of a distinction between a contactless payment card, an iPhone or an Android phone. Just make sure you have a backup payment method.

Bumpety bump! Android Pay is now available in the UK. Points to note:

• No additional authentication per use (you just have to wake the phone, which should avoid accidental payments).
• Up to £30, no pin required, but unlike Apple Pay you can go beyond £30 (up to 100, albeit with PIN).
• No Amex support (yet, I assume).
• Not all credit cards and banks supported.
• At the moment it works with only my Nationwide debit card.

Setup and use is simple. You take a photo of the card, fill in the CVC and then authenticate with the provider, who sends you an SMS message with an authentication code. In practice, use is simple. Wake the phone and touch the terminal with it (and I really do have to be holding the corporate S5 Neo far closer to the terminal than I do with my iPhone).