The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/applying-to-set-up-a-border-control-post-at-your-port-or-airport?utm_source=9a38aa71-bb63-478f-ad11-e641f0de3ab7&utm_medium=email&utm_campaign=govuk-notifications&utm_content=daily