wagstaffes you can use the same email address for more than one account,
I agree that is a consideration for those with more than one giffgaff account, yet I suspect they may be in the minority and it would be an additional option, not an instead of requirement.
The new app utilises Biometric log on and is able to manage multiple accounts. That should alleviate any confusion over login options, at least within the app.
The main platform would benefit from additional options, particularly for those members who rarely if ever visit their account dashboard, except when they need to, if we could make the process easier by using our email address, that would be another tool in the box, for members.