Self-billing is an arrangement between a supplier and a customer. Both customer and supplier must be VAT registered. Rather than the supplier issuing a tax invoice in the normal way, the recipient of the supply raises a self-billing document. The customer prepares the supplier’s invoice and forwards a copy to the supplier with the payment.
If a business wants to put a self-billing arrangement in place it does not have to tell HMRC or get approval from them, but it does have to get its supplier or customer to agree to the arrangement and meet certain conditions.
Source: marcusward.co