| Highway Stops Limited | Extraterritorial | 1989 |
| Hill & Dean PR Limited | Professional & scientific | 2007 |
| Hill Farm Maintenance Limited | Wholesale & retail | 2008 |
| Hillgrove Business Park Management (Phase 4) Limited | Real estate | 2000 |
| Hillgrove Business Park Management Limited | Real estate | 1996 |
| Hillgrove Management Limited | Real estate | 2002 |
| Hilton Limited | Wholesale & retail | 2007 |
| Hissting Property Company Limited | Real estate | 1997 |
| Hitchin British Schools Trust | Arts & recreation | 1991 |
| HM Studios LDN Limited | Other services | 2025 |
| Hobson Technology Limited | Manufacturing | 1987 |
| Hobtec Limited | Construction | 1996 |
| Hoddesdon Dental Surgery Ltd | Health & social care | 2007 |
| Holden Homes (Southern) Limited | Construction | 1984 |
| Hollybush Consulting Limited | Professional & scientific | 2007 |
| Holtwhites Accommodation & Support Services Limited | Hospitality | 2004 |
| Home and Property Developments Limited | Construction | 2005 |
| Home Education Advisory Service | Education | 1997 |
| Home Farm Putteridge Management Limited | Households | 2000 |
| Home Shopping International Limited | Extraterritorial | 1995 |
| Homebuyers Consultants Limited | Financial services | 2007 |
| Homestead Relocation Company Ltd | Real estate | 2024 |
| Honey POT Recordings Limited | Arts & recreation | 2000 |
| Honeyman Clinical Limited | Health & social care | 2025 |
| Hope Living CIC | Other services | 2024 |
| Hopleys Plants Limited | Agriculture & fishing | 1976 |
| Hopwood Welding Services Limited | Manufacturing | 2006 |
| Horizon Contractors Ltd | Construction | 1998 |
| Horizon Development Capital Limited | Financial services | 2019 |
| Horizon Development Finance Limited | Financial services | 2019 |
| Hospice of ST Francis Trading Limited | Wholesale & retail | 2007 |
| Hoss Property Services Ltd | Real estate | 2024 |
| Hot Rims Ltd | Professional & scientific | 2009 |
| Hotel Chocolat Stores Limited | Administrative & support | 2004 |
| Houghton Safety Services Limited | Professional & scientific | 2007 |
| Househusbands Limited | Administrative & support | 2003 |
| HRM Network Limited | Wholesale & retail | 2007 |
| HSD Tech UK Ltd | Wholesale & retail | 2024 |
| Hub Electronics Limited | Wholesale & retail | 2001 |
| Hubano Limited | Wholesale & retail | 2017 |
| Huda Ventures Ltd | Administrative & support | 2025 |
| Hudson Fisher Limited | Wholesale & retail | 2001 |
| Huggins Lane Developments Ltd | Real estate | 2024 |
| Human by Design Ltd | Information & communication | 2021 |
| Hunsdon Garage Ltd | Wholesale & retail | 2005 |
| Hunterlodge Advertising Limited | Professional & scientific | 1994 |
| Hunterlodge Media Limited | Manufacturing | 1993 |
| HW Associates Limited | Professional & scientific | 2004 |
| HYDR8 Limited | Manufacturing | 2026 |
| Hygain Services Limited | Information & communication | 2000 |
| I J Walker Limited | Other services | 2002 |
| I Project Management Limited | Real estate | 2005 |
| I-Reg Consulting Limited | Professional & scientific | 2013 |
| I.G.M. Associates Limited | Real estate | 2002 |
| IA Wiltshire Ltd | Real estate | 2026 |
| IAM Pmpro Ltd | Information & communication | 2023 |
| IAN Cooper Communications Limited | Professional & scientific | 2002 |
| Ibby's Chauffeurs Ltd | Other services | 2021 |
| Ideal Food & Wine Ltd | Wholesale & retail | 2026 |
| Idelo Limited | Health & social care | 1999 |
| Identityy Technology Ltd | Information & communication | 2016 |
| Ifcofield Properties Limited | Construction | 1987 |
| IK Advisory Ltd | Professional & scientific | 2026 |
| Iline Media Ltd | Information & communication | 2006 |
| Imagine Consultancy Services Limited | Information & communication | 2023 |
| IMB Diamond Drilling Ltd | Construction | 2014 |
| IMP Consulting Ltd | Information & communication | 2005 |
| Imraab Limited | Administrative & support | 2004 |
| In-Tech LDN Limited | Wholesale & retail | 2025 |
| Incognito Travel Limited | Transport & logistics | 1989 |
| Independent Funeral Directors' College Limited | Education | 1995 |
| Independent Social Care Assessment Plus Ltd | Health & social care | 2024 |
| Indian Nights (Redbourn) Ltd | Hospitality | 2017 |
| Indobrit Pictures Limited | Extraterritorial | 2000 |
| Indrush Limited | Wholesale & retail | 1981 |
| Industrial Commercial Build Limited | | 1993 |
| Infinite Professional Services Ltd | Information & communication | 2018 |
| Infomark Limited | Wholesale & retail | 1994 |
| Inn on the Park (ST Albans) Limited | Hospitality | 2005 |
| Innovation Electronics Limited | Professional & scientific | 1986 |
| Inqpharm Consumer Health Limited | Administrative & support | 2005 |
| Insite Legal Limited | Professional & scientific | 2023 |
| Inspect Buildings Ltd | Professional & scientific | 2019 |
| Inspire Performance Limited | Professional & scientific | 1994 |
| Instantshare Property Management Limited | Households | 1992 |
| Intcap Limited | Administrative & support | 2007 |
| Integritas Designum Consultants Limited | Information & communication | 1998 |
| Inter MAX Limited | Real estate | 1995 |
| Interactive Ventures Limited | Real estate | 2000 |
| Interlink UK Exports Limited | Wholesale & retail | 1997 |
| Interm ICT Ltd | Extraterritorial | 2003 |
| Interm IT Limited | Information & communication | 2000 |
| Internal Audit Solutions Limited | Professional & scientific | 1997 |
| International Journal of Experimental Pathology | Other services | 1939 |
| International Resource Recovery Company Limited | Professional & scientific | 1996 |
| International Tang SOO DO Federation MOO DUK Kwan Limited | Professional & scientific | 1996 |
| Interplan Network Limited | Information & communication | 1998 |
| IPC Print Limited | Administrative & support | 2008 |
| Iron & Sons Limited | Other services | 2004 |
| Ironcraft Limited | Manufacturing | 1998 |