Pierre, I am not sure I have understood your question correctly but hopefully my answer will be of some use.
Before your organisation can move to Paperless Direct Debit you need to have to have AUDDIS status unless you are working on behalf of an organisation who already has AUDDIS status and will be the party processing the Direct Debits.
There is an AUDDIS rule book that tells you exactly what you need to do in order to set up the process it also includes sample script wording, sample letters etc. I have pasted a link to the AUDDIS website below. You also need to have Bank Account Validation software which validates that the bank account number and sort code are accurate before the DD requests are submitted. There are various different bits of software on the market, some can be integrated into your current system so you can do the validation at point of collection and others allow validation after the event but this is less efficient.
http://www.bacs.co.uk/Bacs/Businesses/DirectDebit/Services/Pages/PaperlessDD.aspx