Great update from @cookywook 
Some additional stats:
We process about £1bn a year through card topups, overwhelmingly driven by users who’ve upgraded from the prepaid card and not switched to bank transfer yet.
The cost of providing card topups to the average upgraded prepaid user is £12/year. Only about 50% of these users actually use card topups (the remainder rely on bank transfer), so the cost for the people who actively use card topups is around £24/year. Obviously, for the new users where we’ve turned off card topups, the cost of putting money into the account is practically zero.
By comparison, it only costs £8/year to provide Monzo’s customer service to a user.
So, it would really help keep Monzo sustainable if we could move more people away from card topups, and towards bank transfer, or even ideally direct deposit of salary (or equivalent like student loan, benefits payments, pension etc).
I’d love to hear from the community - how do think we should do this?