The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.
https://www.gov.uk/guidance/upholding-environmental-standards-if-theres-a-no-deal-brexit?utm_source=81099062-a005-43c9-96f6-59b6b42e2741&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate