| Happy Cats Clinic Ltd | Professional & scientific | 2020 |
| Happy Renew Ltd | Wholesale & retail | 2024 |
| Harkness Roses (Global) Ltd | Professional & scientific | 2022 |
| Harkness Roses (UK Sales) Ltd | Agriculture & fishing | 2022 |
| Harley Street Eyesthetics Ltd. | Health & social care | 2016 |
| Harley Medclinic Ltd | Health & social care | 2024 |
| Harmony Studios Limited | Information & communication | 1997 |
| Harriet Aesthetics Ltd | Health & social care | 2021 |
| Harrison's Electrical, Mechanical & Property Services Limited | Construction | 1998 |
| Harrisons & Associates Limited | Professional & scientific | 2012 |
| Harrisons Accountancy Limited | Professional & scientific | 2008 |
| Harrowden Developments Limited | Construction | 1997 |
| Hawkes Medical Services Limited | Health & social care | 2008 |
| Head Restart Group Ltd | Administrative & support | 2024 |
| Headsail Business Coaching Ltd | Administrative & support | 2020 |
| Healthier Pathways Ltd | Health & social care | 2025 |
| HEAR2LISTEN C.I.C. | Health & social care | 2012 |
| Heasman Differentials Limited | Wholesale & retail | 2019 |
| Heated Plumbing Ltd | Construction | 2025 |
| Helmet Contracting Limited | Construction | 2016 |
| Hemel Access Limited | Construction | 2014 |
| Hemel Hempstead Scaffolding Limited | Construction | 2006 |
| Henry Scott Developments Ltd | Construction | 2020 |
| Henshaw Properties Ltd | Real estate | 2021 |
| Here on Earth Ltd | Real estate | 2025 |
| Heritage & Habitat Ltd | Construction | 2025 |
| Herts Beds and Bucks Mobile Tyre Services Ltd | Wholesale & retail | 2024 |
| Herts Data Cabling Ltd | Construction | 2007 |
| Heue Digital Ltd | Information & communication | 2018 |
| Hickmans Electric Tattoo Limited | Arts & recreation | 2021 |
| Highfield Medical Services Ltd | Health & social care | 2021 |
| Highland Motors (Herts) Limited | Wholesale & retail | 2011 |
| Highthorne | Financial services | 2025 |
| Hijack Productions Limited | Administrative & support | 2016 |
| Hilary Clifford Consulting Ltd | Administrative & support | 2024 |
| Hills Specialised Services Ltd | Water & waste | 2012 |
| Hinge Homes Ltd | Real estate | 2024 |
| Hire Sure Limited | Administrative & support | 2025 |
| HK Food and Beverage Ltd | Hospitality | 2024 |
| HLN Engineering and Trading Limited | Professional & scientific | 2017 |
| Hobbit Hide Aways Ltd | Construction | 2025 |
| Hojo Carpentry Ltd | Manufacturing | 2019 |
| Hollidge Plumbing and Heating Ltd | Construction | 2021 |
| Hollin Green Ltd | Financial services | 2025 |
| Holme Mills Heritage Centre Ltd | Hospitality | 2010 |
| Holmes Doran Ltd | Financial services | 2019 |
| Home Call Health Ltd | Health & social care | 2019 |
| Homegrown Productions Ltd | Arts & recreation | 2026 |
| Honeybee Interior Design Ltd | Real estate | 2022 |
| Hope-Stone Limited | Information & communication | 1996 |
| Hopi Allard Limited | Information & communication | 2017 |
| Hopkin Murray Beskine Limited | Professional & scientific | 2012 |
| Hornbyecom Ltd | Wholesale & retail | 2023 |
| Horseshoe PUB and Dining Ltd | Hospitality | 2025 |
| Horsman Properties Ltd | Real estate | 2021 |
| Horsmanx Ltd | Information & communication | 2023 |
| House of Eden Management Limited | Real estate | 2022 |
| HR Consultants Ltd | Professional & scientific | 2006 |
| HSH Ltd | Information & communication | 2008 |
| Hulstrom Digital Media Limited | Administrative & support | 2013 |
| Hultsteins UK Limited | Manufacturing | 2007 |
| HUM-3 Ltd | Professional & scientific | 2020 |
| Human Resource Consultants Ltd | Professional & scientific | 2001 |
| HY Social Ltd | Professional & scientific | 2021 |
| Hypercrypt Solutions Ltd. | Information & communication | 2012 |
| Icandy World Limited | Wholesale & retail | 1933 |
| Icmap Ltd | Manufacturing | 2021 |
| Icon Artist Management Ltd. | Professional & scientific | 2015 |
| Icqs Limited | Professional & scientific | 2025 |
| ICS Consultancy Limited | Professional & scientific | 2004 |
| Ifon-Touch UK Ltd | Wholesale & retail | 2015 |
| Ignite Studios Biggleswade Limited | Hospitality | 2025 |
| Ikarus Engineering (Holdings) Ltd | Financial services | 2014 |
| Ikarus Engineering Limited | Administrative & support | 1997 |
| Imago Portraits Limited | Professional & scientific | 2003 |
| Imperial Brickcutting Ltd | Manufacturing | 2024 |
| Implant Expertise Ltd | Health & social care | 2015 |
| IN Reach Estates Limited | Real estate | 2025 |
| Independent Personal Financial Management Limited | Financial services | 2003 |
| Individual Artist Management Limited | Arts & recreation | 2016 |
| Individual Productions Ltd | Arts & recreation | 2023 |
| Infant Feeding Specialist Services Ltd | Health & social care | 2024 |
| Influx Technology EV Ltd | Professional & scientific | 2023 |
| Information Security Systems Installations Limited | Construction | 2001 |
| Injoniso Consulting Services Ltd | Information & communication | 2025 |
| Inlinks Optimization Ltd | Information & communication | 2019 |
| Innovative Perspectives Limited | Professional & scientific | 2024 |
| Insight Automation Limited | Manufacturing | 2002 |
| Inspiral Management Ltd | Professional & scientific | 2002 |
| INTERFR8 UK Freight Solutions Ltd | Administrative & support | 2016 |
| Interiors Redfined Limited | Professional & scientific | 2025 |
| Intriguing Industries Ltd. | Extraterritorial | 2021 |
| Invirra Ltd | Professional & scientific | 2025 |
| Ipfm Limited | Professional & scientific | 2003 |
| IREPAIRS4U Ltd | Other services | 2012 |
| ISG Property Limited | Real estate | 2005 |
| ISOL8 Pilates Ltd | Other services | 2025 |
| ISOP1 Ltd | Arts & recreation | 2025 |
| Issi Holdings Limited | Financial services | 2024 |
| Ivel Mill Residents' Association Limited | Households | 1986 |