If anyone's looking for API access to UK high street banks: https://teller.io
Thanks! Founder here. Currently in private beta, but if you're with Santander, Nationwide, RBS, Natwest, Ulster Bank NI, or IOM Bank I can give you access - sg@teller.io.
Also, isn't it going to be reasonably fragile? There's nothing stopping the banks (other than [in my experience] their general inability to make technical changes at a reasonable pace) pushing an update and breaking old API clients, right?