VATSM5310 - Simplifications: processing of goods: background
Member States operate a limited simplification to cover intra-EC movements of processed goods. The main requirement is that the goods must be sent by the processor to the person (the principal) who ordered the processing. However, the raw materials do not have to originate from the principal’s Member State. The simplification cannot be used if the processed goods are not dispatched to the principal. So if the principal, say, makes an onward supply of the processed goods in the Member State of process, the simplification does not apply and they may be required to register in that Member State in respect of the supply.
For its part, the processor makes a supply of services on which the principal will normally be required to account for VAT as a reverse charge. For further information about this see the manual covering the place of supply of services (VATPOSS). The processor is not required to complete an EC sales list.