| Headbase Limited | Real estate | 2001 |
| Headline London Ltd | Professional & scientific | 2012 |
| Health Outcomes & Market Access Solutions Ltd | Professional & scientific | 2010 |
| Heart Residential Ltd | Real estate | 2025 |
| Heartsynch Limited | Health & social care | 2006 |
| Heath DRY Cleaners Limited | Other services | 2026 |
| Heather RTM Company Limited | Extraterritorial | 2026 |
| Heirloom Haus Limited | Wholesale & retail | 2025 |
| Helios Cloud Tech Ltd | Wholesale & retail | 2018 |
| Helix Corporate Management Limited | Hospitality | 2012 |
| Hemlens Ltd | Professional & scientific | 2011 |
| HEP Bikes Ltd | Wholesale & retail | 2025 |
| Hertfordshire Paving and Landscaping Ltd | Administrative & support | 2020 |
| Hertribe Ltd | Administrative & support | 2025 |
| Herts Construction Services Ltd | Construction | 2016 |
| Hetherington & Field Associates Limited | Professional & scientific | 2011 |
| Hevac Services Ltd | Construction | 2026 |
| Hexaworld Creations Ltd | Wholesale & retail | 2025 |
| Hexion HR Solutions Limited | Professional & scientific | 2012 |
| Hibabox Ltd | Information & communication | 2019 |
| Hibabox Solution Ltd | Information & communication | 2019 |
| High Flying Construction Limited | Construction | 2020 |
| Highland Properties 5 Ltd | Real estate | 2023 |
| Highscreen Solutions Limited | Information & communication | 1997 |
| Hilldan Services Limited | Information & communication | 2025 |
| Hillside Estates Limited | Real estate | 2003 |
| Hillside Freehold Company Limited | Households | 2014 |
| Hillside Mansions Residents Management Company Limited | Households | 2009 |
| Hinoptics Ltd | Health & social care | 2019 |
| Hire and Clean Ltd | Administrative & support | 2024 |
| Hire&Go Services Ltd | Transport & logistics | 2018 |
| Historic Aero Engineering Ltd | Manufacturing | 2021 |
| Historic Tours of England Limited | Administrative & support | 2022 |
| Hitt Oak Limited | Construction | 2003 |
| Hiver Ltd | Wholesale & retail | 2018 |
| HM Recruit Ltd | Administrative & support | 2022 |
| Holdeans Limited | Other services | 2023 |
| Holly RTM Company Limited | Extraterritorial | 2026 |
| Holyfort Ltd | Health & social care | 2023 |
| Home Counties Flooring Limited | Construction | 2017 |
| Home Fixings Limited | Other services | 2021 |
| Home Warmth Ltd | Construction | 2011 |
| Homemade Harmony Treats Limited | Wholesale & retail | 2024 |
| Honeypot Enterprises Limited | Real estate | 2005 |
| Hoopers Mews Management Company Limited | Households | 2002 |
| Hornbees Waste Management Limited | Administrative & support | 2011 |
| House of Challah Ltd | Information & communication | 2026 |
| House of Watkins Ltd | Wholesale & retail | 2023 |
| HRH Independent Property Surveys Ltd | Professional & scientific | 2025 |
| HRJ Cleaning Services Ltd | Administrative & support | 2025 |
| Hrka Limited | Health & social care | 2015 |
| Hsbn Limited | Households | 2021 |
| HSL Properties Limited | Real estate | 1998 |
| Hugh Bethell Limited | Health & social care | 2014 |
| Hurst Mailagent Limited | Information & communication | 2003 |
| Hydrangea RTM Company Limited | Extraterritorial | 2026 |
| Hyelite Ltd | Information & communication | 2021 |
| Hyfi Private Wealth Limited | Financial services | 1983 |
| Hypericum RTM Company Limited | Extraterritorial | 2026 |
| IAH Lettings Limited | Real estate | 2020 |
| Iberia Pbsa Ltd | Real estate | 2024 |
| Icreate Designs Limited | Professional & scientific | 2013 |
| Igem Communications Ltd | Information & communication | 2016 |
| Ikhi Ltd | Health & social care | 2018 |
| Imech Limited | Construction | 2010 |
| India Garden (Bushey) Ltd | Hospitality | 2018 |
| Indigo Locke Consulting Ltd | Professional & scientific | 2022 |
| Infection Specialist Services Limited | Health & social care | 2021 |
| Infinite Consulting Group Ltd | Information & communication | 2022 |
| Infinity Designer Ltd | Arts & recreation | 2024 |
| Infinity Resources Limited | Professional & scientific | 2015 |
| Infobits Limited | Information & communication | 2011 |
| Inhouse Developments (UK) Limited | Construction | 2008 |
| Innate AI Ltd | Information & communication | 2025 |
| Inner Landing Ltd | Health & social care | 2024 |
| Inner Works Therapy Ltd | Education | 2021 |
| Innovative Medical Resources Limited | Wholesale & retail | 2022 |
| Innovativeuk Ltd | Information & communication | 2021 |
| Innovent Limited | Professional & scientific | 2013 |
| Innthrall Limited | Hospitality | 2003 |
| Inphocus Limited | Professional & scientific | 2024 |
| Insight Technology Systems Ltd | Professional & scientific | 2026 |
| Integrated Development Consultants Ltd | Professional & scientific | 2016 |
| Integrated Engineering & Aerospace Limited | Professional & scientific | 2005 |
| Intelletec Holdings Ltd | Administrative & support | 2015 |
| Intelletec Limited | Administrative & support | 2013 |
| Intercom Genius Ltd | Manufacturing | 2020 |
| Interlife Limited | Administrative & support | 2016 |
| International Academy of Languages and Narrative Art Limited | Professional & scientific | 2025 |
| Interproperty Systems Limited | Information & communication | 1983 |
| Invagloria Limited | Professional & scientific | 1971 |
| Investment Consultancy Limited | Professional & scientific | 2024 |
| Invia Homes Limited | Real estate | 2022 |
| Ioana Trans Ltd | Transport & logistics | 2022 |
| Iremotecontrol Ltd | Information & communication | 2014 |
| Irradiant Ltd. | Information & communication | 2011 |
| Italian Coffee Pizzeria Ltd | Transport & logistics | 2021 |
| IVY House RTM Company Limited | Households | 2025 |
| J H Video Limited | Professional & scientific | 2014 |
| J J MAX Ltd | Administrative & support | 2011 |