What do I do, if I do not have all the necessary information for a declaration eg seal number or container number?
You are responsible for ensuring your freight forwarder gives you this information. If the goods are being exported from Approved premises Inland, any requirement to seal containers will be part of your Approval conditions. If the seals to be used are provided from your stock, it should be possible to specify which seal is to be used, even if a Remote Packer actually fixes it to the container after loading. In this way, it should be possible to enter the seal number as part of your declaration from the outset, and to add the container number later, when the Remote Packer has notified you of it.
