The Direct Debit Guarantee is not something NRTH created. It's a UK wide protection offered by every bank and building society that accepts Direct Debits.
Here's what it guarantees:
Advance notice. If the amount, date, or frequency of a Direct Debit changes, the payer must be notified in advance.
Instant refund. If a payment is made in error, or without proper authorisation, the payer's bank will immediately refund the full amount. The payer doesn't need to prove anything.
Right to cancel. The payer can cancel a Direct Debit at any time by contacting their bank.
This guarantee exists to give people confidence in Direct Debit. And it works. Over 4.5 billion Direct Debit payments are processed in the UK every year.