| Hase Consultants Limited | Professional & scientific | 2017 |
| Have YOU Tried Turning IT OFF and Back on Again Ltd | Information & communication | 2010 |
| Hazard Lines Limited | Construction | 2017 |
| Hazel Orchard Limited | Real estate | 1997 |
| HCI Accountancy Limited | Professional & scientific | 2014 |
| HCS Films Limited | Information & communication | 2022 |
| Headera Limited | Information & communication | 2009 |
| Healthfare Ltd | Wholesale & retail | 2015 |
| Heavy Duty Towing Ltd | Transport & logistics | 2023 |
| Hegemonist Ltd | Professional & scientific | 2019 |
| Heila Wellness Ltd | Health & social care | 2026 |
| Heirs & Graces (Tring) Limited | Education | 2004 |
| Hekuda Creative Ltd | Information & communication | 2018 |
| Helen Thompson Consulting Ltd | Professional & scientific | 2022 |
| Helephant Holdings Ltd | Real estate | 2020 |
| Heliconia Technology Limited | Professional & scientific | 2012 |
| Henrique LPS Limited | Information & communication | 2022 |
| Here Comes ROD Ltd | Information & communication | 2011 |
| Hermes Solutions Ltd | Other services | 2011 |
| Hertfordshire Home Improvements Limited | Construction | 2011 |
| Herts PAT Testing Ltd | Professional & scientific | 2007 |
| Hexagon Networks Ltd | Information & communication | 2020 |
| Hiddnfield Limited | Information & communication | 2022 |
| High Contrast Films Limited | Information & communication | 2017 |
| Highbirch Limited | Hospitality | 2016 |
| Highcurve Limited | Information & communication | 2008 |
| Hill Communications Limited | Professional & scientific | 1992 |
| Hill Media Limited | Information & communication | 1990 |
| Hilltop Accounting Services Limited | Professional & scientific | 2002 |
| Hilltop Fire Protection Ltd | Public administration | 2025 |
| Hogs on Film C.I.C. | Wholesale & retail | 2024 |
| Home Farm Management Company (Tring) Limited | Households | 1995 |
| Home Property Professionals Ltd | Real estate | 2019 |
| Home Technology Contracts Limited | Information & communication | 2010 |
| Honeycomb Hair and Beauty Limited | Other services | 2012 |
| Honeyfitz Ltd. | Professional & scientific | 2019 |
| Hope and Hart Limited | Manufacturing | 2013 |
| Hope's Carpets & Flooring Limited | Wholesale & retail | 2003 |
| Horsecroft Consulting Limited | Professional & scientific | 2017 |
| Horsecroft Property Limited | Real estate | 2018 |
| Hortus Illuminations Ltd | Manufacturing | 2019 |
| Hotel Bulletin Ltd | Information & communication | 2004 |
| Hotel Data Limited | Information & communication | 2001 |
| House of Risk Limited | Professional & scientific | 2022 |
| Houser Lawrence Limited | Information & communication | 2019 |
| HPZ.3 Ltd | Financial services | 2007 |
| HR Inspire Ltd | Administrative & support | 2012 |
| HR Inspire Trustee Limited | Extraterritorial | 2025 |
| HR Project Links Limited | Administrative & support | 2010 |
| HRI Property Services Limited | Hospitality | 2015 |
| HTA Digital Ltd | Information & communication | 2026 |
| HTC Carpentry Ltd | Manufacturing | 2021 |
| HTF Management Company Ltd | Real estate | 2019 |
| Huel Limited | Manufacturing | 2012 |
| Hymnia Ltd | Wholesale & retail | 2024 |
| I Musicanti Limited | Extraterritorial | 2012 |
| Icknield Enterprises Limited | Real estate | 2020 |
| Icknield Holdings Limited | Professional & scientific | 2016 |
| Icknield Villas Management Company Limited | Households | 1989 |
| Ignorable Systems Ltd | Information & communication | 2023 |
| IJB Ltd | Manufacturing | 2018 |
| Im-Wolf Ltd | Professional & scientific | 2023 |
| Image Decorating Ltd | Construction | 2024 |
| Image House Associates Limited | Professional & scientific | 2009 |
| Images Decorating Ltd | Construction | 2024 |
| Images Decorating Services Limited | Construction | 2015 |
| Imeshh Ltd | Manufacturing | 2018 |
| Impex Data Limited | Information & communication | 1995 |
| Impulse Consulting Limited | Professional & scientific | 2010 |
| IN & OUT Developments Ltd | Real estate | 2011 |
| Incubator Properties Ltd | Real estate | 2010 |
| Independent Investigator Ltd | Professional & scientific | 2025 |
| Indovara Limited | Professional & scientific | 2024 |
| Infinity Health Limited | Information & communication | 2013 |
| Infinnerty Designs Limited | Administrative & support | 2013 |
| Infrapreneur Ltd | Other services | 2017 |
| Innovation Unboxed (UK) Limited | Administrative & support | 2021 |
| Inspired Crew Ltd | Administrative & support | 2024 |
| Integral Plumbing and Heating Ltd | Construction | 2026 |
| Integrated BI Solutions Ltd | Information & communication | 2017 |
| Integrity Registration Limited | Information & communication | 2008 |
| Intrapreneur Coaching LLP | | 2019 |
| Intrapreneur Ltd. | Professional & scientific | 2013 |
| Intrepid Ltd. | Information & communication | 2010 |
| Invictus Management Consultancy Ltd | Professional & scientific | 2024 |
| IPH Services Ltd | Information & communication | 2025 |
| Iquilt Limited | Wholesale & retail | 2008 |
| Isalie Bar and Event Managment Limited | Hospitality | 2014 |
| Isalie Limited | Hospitality | 2009 |
| Isculpt Limited | Manufacturing | 2016 |
| Isolutions International Ltd | Wholesale & retail | 2017 |
| Isosceles Medical Writing Ltd | Health & social care | 2018 |
| Isotechnic Limited | Professional & scientific | 2018 |
| IT Aint What IT Aint Limited | Hospitality | 2025 |
| Ithaca-Pavilion Limited | Information & communication | 2008 |
| Iuvoesa IT Solutions Ltd | Information & communication | 2018 |
| Ivnet Limited | Information & communication | 2007 |
| Ivrg Ltd | Financial services | 2017 |
| Ivrg Property Ltd | Real estate | 2022 |
| J Allen Rail Ltd | Transport & logistics | 2013 |