Source is here.
As of June 2020, the following 21 companies supply connections into HSCN.
AdEPT Technology Group
BT
CANCOM UK Managed Services
CenturyLink (Lumen)
Convergence (Group Networks)
Daisy Corporate Services Trading
Exponential-e
Gamma Telecom
High Speed Office
IQVIA
IT Professional Services
KCOM Group
MLL Telecom
Node 4
NYNET
Piksel
Redcentric Solutions
The Networking People
UKFast.net
Updata Infrastructure (UK)
Virgin Media Business
The following 2 companies are being onboarded.
GTT (Interoute)
Telefonica UK