user credentials for UK efiling

Hi All,

For efiling in UK, we maintain user credentials in table t5gefcredentials or in through IMG->PM->PA->payroll data-> efiling GB-> maintain user credentials.

This user ID is mostly a combinaiton of alphanumerics.  Is there any criteria that needs to be followed to maintain this user ID?   I came to know that HMRC provides user ID only in numerics.  In SAP, what criteria is followed to maintain the user ID in alphanumerics?. Also password is compulsory to maintain?

Please can you explain more on this?

Thanks and Regards

Latha