[Milner08]

They seem to be operating very well with the 2000 services (the number doesn't seem to have changed much in the last few years which is interesting, despite them adding new features, etc).

The domain is obviously very complex as its not just a ledger, but risk, loans, overdrafts, savings, etc as well as premium offerings, interacting with different payments networks like FasterPayments and Mastercard. Then there are the budgeting features, payments between friends, support system (Which is probably quite complex in its self), card issuing, internal dashboards and metric services, etc, etc, etc. I can easily see how this gets to 2000 services and I didn't even begin to think about the business accounts, US accounts, etc.