| Herts & Cambs Ground Maintenance Limited | Administrative & support | 2009 |
| Herts & Cambs Woodburners Limited | Construction | 2024 |
| Hetty Lintell Limited | Professional & scientific | 2020 |
| Heydon Garden Village Ltd | Real estate | 2021 |
| Heydon Services Limited | Professional & scientific | 2005 |
| Hhatch Solution Ltd | Professional & scientific | 2021 |
| Highbury Place Limited | Households | 2000 |
| Hill Express Ltd | Wholesale & retail | 2026 |
| Hill View Building Limited | Construction | 2024 |
| Hillberry Court (Bushey) Limited | Real estate | 2000 |
| Hippo Holdings Limited | Real estate | 2016 |
| Historic Restoration London Limited | Construction | 2022 |
| History Matters Tours Ltd | Administrative & support | 2025 |
| Hitwrap Limited | Hospitality | 2021 |
| Hive Systems Limited | Professional & scientific | 2002 |
| Hive Technologies Group Limited | Manufacturing | 2018 |
| Hklandscapingsolutions Ltd | Administrative & support | 2024 |
| HMP Holloway Ltd | Arts & recreation | 2025 |
| Hmrgs Ltd | Financial services | 2022 |
| Hmss Investments Limited | Real estate | 2024 |
| Hobson Avenue Management Company Limited | Households | 2017 |
| Hockwold Holdings Limited | Households | 2024 |
| Hoem Properties Limited | Real estate | 2023 |
| Holdings JDH Ltd | Administrative & support | 2026 |
| Holly Atkin Limited | Other services | 2016 |
| Holmes Solutions Ltd | Wholesale & retail | 2025 |
| Home Help Services Limited | Health & social care | 2026 |
| Horizon Creative Ltd | Professional & scientific | 2017 |
| Horse Racing Advisory Services Limited | Professional & scientific | 2019 |
| Horwood Pharma Consulting Ltd | Extraterritorial | 2021 |
| Hot Air Aviation Limited | Arts & recreation | 2025 |
| Hotc Ltd | Financial services | 2009 |
| Hotel Chocolat EU Retail Limited | Wholesale & retail | 2017 |
| Hotel Chocolat Group Limited | Financial services | 2013 |
| Hotel Chocolat Limited | Manufacturing | 1993 |
| Hotel Chocolat Retail Ltd | Wholesale & retail | 2009 |
| Hotel FM Ltd | Administrative & support | 2025 |
| Howson Wholesale Ltd | Wholesale & retail | 2025 |
| HP Solar Limited | Energy | 2013 |
| Hpsb Limited | Real estate | 2022 |
| HQ Racing Syndicate Limited | Administrative & support | 2021 |
| HS Elsom Ltd | Professional & scientific | 2010 |
| Hugh Wood Consulting Ltd | Professional & scientific | 2019 |
| Hugo George Kohl Richardson Limited | Wholesale & retail | 2011 |
| Human Energy Optimisation Ltd | Professional & scientific | 2024 |
| Humankind Innovations Limited | Extraterritorial | 2025 |
| Hunny Holidays Limited | Hospitality | 2024 |
| Hunter Camp Homes Limited | Real estate | 2017 |
| Hunters Mews Residents Limited | Households | 1997 |
| Huntingfield Limited | Agriculture & fishing | 2019 |
| Hunts Tiling & Decorating Ltd | Construction | 2019 |
| Hurricane 501 Operations LLP | | 2018 |
| Hutsul Craft Ltd | Construction | 2024 |
| Hydex Solutions Limited | Wholesale & retail | 2008 |
| I J Davidson Consulting Limited | Professional & scientific | 2015 |
| I.C.E. Plumbing and Heating Limited | Construction | 2025 |
| I.M.S. Air Conditioning Limited | Real estate | 1985 |
| Ibaqt Ltd | Real estate | 2015 |
| Ibix Innovate Limited | Health & social care | 2011 |
| Ibix Insight Limited Liability Partnership | | 2005 |
| Icknield Limited | Professional & scientific | 2003 |
| Icknield Stores Ltd | Wholesale & retail | 2012 |
| Iclip Limited | Manufacturing | 2016 |
| Idea Innovative Drug European Associates Limited | Professional & scientific | 1994 |
| Idea Regulatory Limited | Professional & scientific | 2017 |
| Ifixitrepairs-Royston Ltd | Manufacturing | 2019 |
| IGO Management Limited | Professional & scientific | 2022 |
| Iiot Consulting Ltd | Information & communication | 2022 |
| Ikang Health Ltd | Health & social care | 2015 |
| Impact Focus Ltd | Professional & scientific | 2023 |
| Impartech Limited | Information & communication | 2008 |
| Impeccable Property Developments Limited | Construction | 2015 |
| Impeccable Solutions Limited | Professional & scientific | 2008 |
| Imperia Cleaning Group Ltd | Other services | 2024 |
| Impress Promotions (Midlands) Limited | Wholesale & retail | 2007 |
| Impulse Electrical Testing and Installation Limited | Construction | 2026 |
| IMV Europe Limited | Wholesale & retail | 2013 |
| Inaspace Rooms Ltd | Construction | 2022 |
| Incar Additions Limited | Administrative & support | 2009 |
| Indegro Limited | Professional & scientific | 2013 |
| Independent Project Engineering Limited | Professional & scientific | 1983 |
| Indi + EVE Beauty & Co Ltd | Other services | 2022 |
| Indigo Fields Limited | Extraterritorial | 2003 |
| Infinite Leadership Ltd | Professional & scientific | 2021 |
| Infinity Fiction Limited | Information & communication | 2024 |
| Informatics Insider Ltd | Information & communication | 2023 |
| Informatics Limited | Information & communication | 2021 |
| Ingenium Business Development Ltd | Administrative & support | 2020 |
| Ingot Digital Ideas Limited | Information & communication | 2014 |
| Innerplace Limited | Other services | 2002 |
| INNOV8TV Limited | Professional & scientific | 2020 |
| Innovativehse Limited | Professional & scientific | 2017 |
| Innovorsa Limited | Professional & scientific | 2009 |
| Insink Plumbing & Heating Limited | Construction | 2017 |
| Instant Teamwork Limited | Professional & scientific | 2008 |
| Institutional Distribution Limited | Extraterritorial | 2013 |
| Intacloud Ltd | Information & communication | 2014 |
| Integration Partners Limited | Professional & scientific | 2026 |
| Intelligent Integration Ltd | Administrative & support | 2015 |
| Intellikel Ltd | Professional & scientific | 2025 |