I use Online Services for other government departments. Can I use the same User ID and password for ATWD XML?
Yes if you initially registered as an 'Organisation' at the Government Gateway.
However, if you already have a Government Gateway User ID and password for use with services relating to you as an 'Individual User', eg PAYE Self Assessment or Council Tax, then you will be unable to use that User ID and password for any HMRC Online Service. This is because the Government Gateway differentiates between services relating to you and services relating to the organisation you work for.
If you only have an 'Individual' gateway user account you will need to register again to obtain a new User ID representing your organisation or employer.