I just did this with a loan of DH' s. Not as a surprise. I was able to log into manage the loan online with the loan account number and either just our postcode or his dob. There was an option to request settlement figure. You could view this but it also sent an automated letter so that might be a give away for you!
This was with black horse but I have noticed out Natwest mortgage can be managed the same way. I suppose it's less restricted than regular online banking as it is only borrowed money you are dealing with.