[tialaramex]

You don't need credit to have a contactless debit card, they're just locked down to require online transactions so that it's impossible to go overdrawn. In normal operation a TfL gate is online (ie able to talk to your card issuer) so it can work with any type of card.

[vertex-four]

Sure, but many basic bank accounts (those available to people with extremely poor credit history and no income) don't have a contactless debit card anyway, such as the one Bank of Scotland does: https://www.bankofscotland.co.uk/bankaccounts/compare-curren...

[jon-wood]

TfL gates aren't online in anything but the most basic way - the first time you use a contactless card on TfL each day they'll place a hold for 10p to verify the card is valid. They then modify that to request the total cost of travel for the previous day after that.