I'm not entirely sure I know what you mean when you say your login and password are automatically generated? If you mean they are automatically filled for you then the chances are that you changed your password but did not update it in your keychain. If you're using the same apple ID on the Mac and iPad and use the iCloud it's likely that the same incorrect saved password is shared across the two devices causing you the same problem on the two devices.

I would suggest you do the following. Go to BA.com and click on the "Forgotten Pin/Password?" link just below the "Log in" button. Enter your user ID or Exec Club number and follow the instructions. Once you've reset the password log in again and tell Safari to update the saved password.

When you click on the "Forgotten Pin/Password?" link it will send you an email. If you don't receive the email (after checking junk/spam folders) then you ought to get concerned as it may indicate that someone has hacked your account and changed the email address. If this happens call BA immediately.