Adrian wrote:

So - when WILL the official licenced busker pitches be equipped with Oyster
readers, so you can use your prepay credit to donate to them?

Singapore already makes that possible - their Oyster-equivalent cards
(ezLink) can be touched against charitable donation machines in shopping
centres. There was a video playing saying how great the chairty was,
and then touchpads for donating $1, $5 and $10 from your ezLink card.

ezLink isn't really comparable to Oyster though, it works as you'd
expect, and works first time. It also gives you credit/discount for
using interconnecting public transport services (ie if you took a bus to
your MRT/tube station, took the tube/MRT, then a bus from the
destination station to your final destination, the bus + train + bus
journey would cost less than a single train and two single bus journeys
alone.