The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/uk-product-safety-and-metrology-in-a-no-deal-brexit?utm_source=349969a6-456d-431a-9be9-161816ac1bf6&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate