The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/living-in-the-eu-prepare-for-brexit?utm_source=eef9b851-df07-460b-8ec3-1e894ab2a6e7&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate