Apologies, I probably jumped the gun a bit in my presentation yesterday. Just for the sake of full transparency, here is what I said yesterday:
- we’re beginning non-staff testing of overdrafts next week
- the pricing we are testing is 50p/day with a £20 buffer and no interest rate
A full blog post explaining how we arrived at that conclusion, how testers are picked, etc is coming next week 
Thanks for holding us to a high standard @alexs!