The customer authorization (provided in the link you clicked) is out of date, and does not entitle you to use the Blended Threat service.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/public-sector-procurement-after-a-no-deal-brexit?utm_source=d994d3cd-d2a1-4459-a950-f0ea0b25f7cd&utm_medium=email&utm_campaign=govuk-notifications&utm_content=immediate