| HardSoft Ltd | Hertfordshire |
| Hardware Associates | |
| HARE Digital Ltd | |
| Haredata Electronics | North Yorkshire |
| Harford Control Ltd | Wiltshire |
| Hark 2 Ltd | Leicestershire |
| Hark Systems Ltd | West Yorkshire |
| Harlequin Software Ltd | Wiltshire |
| Harleys | |
| Harmonic Software Systems | West Sussex |
| Harmony Internet | |
| Harmonypark | |
| Harness Data Intelligence Ltd | |
| Harness Therapeutics Ltd | |
| Harper Adams University | |
| Harper Office | Greater London |
| Harper Recruitment Group | |
| Harrison Mann | West Yorkshire |
| Harrisons Finance & Marketing, LLP | |
| Harrogate Computers | North Yorkshire |
| Harrogate Web Solutions | North Yorkshire |
| Harrowden IT (Kintyre) Ltd | Highland |
| Hartpury University and Hartpury College | |
| Haruko Ltd | Greater London |
| Harvey IT Services | |
| Harvey Morton Digital | South Yorkshire |
| Harwell Innovation Centre | |
| Harwin plc | Hampshire |
| HASH | |
| HashRoot Ltd | |
| Haslam IT | |
| HAStech Solutions | |
| Hastee Technologies Ltd | Greater London |
| Hasty Head Ltd | |
| Hatch Enterprise | |
| Hatch House Ltd | |
| Hatch-House Ltd | |
| Haud Systems Ltd | |
| Haulmont | |
| HaulTech | Staffordshire |
| HausBots Ltd | |
| Haven Automation Simulation | Swansea |
| Haven Systems Ltd | Pembrokeshire |
| Havilah Blockchain Studio | |
| Having Computer Problems..? | Cambridgeshire |
| Hawker Electronics Ltd | West Midlands |
| Hawkeye Design Ltd | |
| Hay Sysytems Ltd | West Lothian |
| Haych Enterprises Ltd | |
| Haydon Communications | Essex |