| Howlin' Hound Productions Ltd | Arts & recreation | 2014 |
| Howling Wolf Media Ltd | Professional & scientific | 2016 |
| HOX Design Ltd | Professional & scientific | 2014 |
| Hoxtonlab Ltd | Information & communication | 2011 |
| Hppn Ltd. | Information & communication | 2021 |
| Hppn Studios Ltd | Information & communication | 2026 |
| HR Engineering Limited | Wholesale & retail | 2013 |
| HR Photography Limited | Professional & scientific | 2002 |
| HSA & Co (Newmarket) Ltd | Professional & scientific | 2022 |
| Hugh Hodge Limited | Agriculture & fishing | 1976 |
| Hughes Products Limited | Administrative & support | 2009 |
| Hugo Lascelles Bloodstock Limited | Professional & scientific | 2019 |
| Hunter Knowles Search Limited | Administrative & support | 2024 |
| Hunter Scientific Limited | Manufacturing | 1995 |
| Hutch London Limited | Real estate | 2016 |
| Hutton Consulting Services Limited | Administrative & support | 1976 |
| HVR Jackson & Sons Limited | Construction | 2016 |
| Hyll Road Estate Management Limited | Households | 1977 |
| I Autos Trade Ltd | Wholesale & retail | 2025 |
| I Structure Limited | Professional & scientific | 2026 |
| IAN Baldwin Financial Services Ltd | Financial services | 2020 |
| IAN Wolter Sculpture Limited | Arts & recreation | 2024 |
| Ibiostratix Ltd | Wholesale & retail | 2025 |
| Ibusiness Ltd | Extraterritorial | 2005 |
| Ice & JAR Limited | Administrative & support | 2025 |
| Iceni Properties Limited | Real estate | 1998 |
| ID8 Verify Limited | Administrative & support | 2022 |
| Ievent Safety Services Ltd | Public administration | 2024 |
| IFA Properties (Cornwall) Ltd. | Financial services | 2021 |
| Ifield Technology Limited | Financial services | 2019 |
| Ignite London Limited | Hospitality | 2021 |
| Ignite New Media Limited | Administrative & support | 2001 |
| Ignyte Digital Limited | Professional & scientific | 2015 |
| II Ltd | Extraterritorial | 2008 |
| Illuceo Limited | Information & communication | 2004 |
| Illumos Ltd | Manufacturing | 2024 |
| Illustrious Epic Property Co Ltd | Real estate | 2018 |
| Immediate Label Limited | Administrative & support | 2008 |
| Immediate Labels Limited | Extraterritorial | 2009 |
| Imogen Pope London Ltd | Manufacturing | 2022 |
| Imprint (Holdings) Limited | Professional & scientific | 1992 |
| Imprint Business Systems Limited | Information & communication | 1985 |
| IMT Aviation Limited | Transport & logistics | 2004 |
| IN Partnership With Limited | Professional & scientific | 2007 |
| INCUB8 Solutions Ltd | Professional & scientific | 2019 |
| Independent Pet Clinics Limited | Professional & scientific | 2024 |
| Indie Consulting Ltd | Professional & scientific | 2018 |
| Indigo Ventures Limited | Professional & scientific | 1995 |
| Infoness 327 Limited | Administrative & support | 2020 |
| INK Solve.Com Ltd | Wholesale & retail | 2018 |
| Inky Fingers Ltd | Wholesale & retail | 2024 |
| INM Consulting Limited | Information & communication | 2019 |
| INM Solutions Limited | Information & communication | 2025 |
| Inmersionuk Limited | Education | 2018 |
| Innomed Holdings Limited | Wholesale & retail | 2004 |
| Innotec Limited | Information & communication | 2001 |
| Integrated Discovery Consulting Limited | Professional & scientific | 2025 |
| Intellima LLP | | 2011 |
| Intellima Services Ltd | Professional & scientific | 2025 |
| Interior Design Deconstructed Ltd | Education | 2024 |
| Intermodal Transportation Limited | Construction | 2000 |
| International Jatt Forum | Education | 2003 |
| International Language Teaching Services Limited | Information & communication | 2005 |
| Invention Interactive Limited | Professional & scientific | 2010 |
| Invert Ltd | Professional & scientific | 2019 |
| Ionpure Technologies Ltd | Water & waste | 2003 |
| IPC Limited | Professional & scientific | 2025 |
| IPM Fire & Security Ltd | Construction | 2018 |
| Iqoniqe Ltd | Administrative & support | 2020 |
| Iresoft Ltd | Transport & logistics | 2024 |
| IS3 Associates Ltd | Professional & scientific | 2026 |
| ISK London Limited | Administrative & support | 2026 |
| Island Pacific (UK) Limited | Information & communication | 2007 |
| Islay Troon Ltd | Real estate | 2025 |
| Isogenica Limited | Professional & scientific | 1998 |
| Issy Care Ltd | Health & social care | 2022 |
| It&S Cambridge Ltd | Health & social care | 2024 |
| Itchen Stoke Manor Ltd | Real estate | 2025 |
| Ixone Limited | Professional & scientific | 2012 |
| J & J Anderson Limited | Information & communication | 2012 |
| J B L Consulting Limited | Professional & scientific | 2013 |
| J Bates Financial Services Limited | Professional & scientific | 2016 |
| J Germeney Electrical Services Ltd | Construction | 2014 |
| J Johnson Plumbing & Heating Limited | Construction | 2024 |
| J P Properties & Maintenance Limited | Real estate | 2025 |
| J Phipps Barbering Ltd | Other services | 2025 |
| J&K Interiors Limited | Other services | 2020 |
| J.Heald Coaching Education Ltd | Education | 2019 |
| J.Heald Coaching Juniors Limited | Arts & recreation | 2014 |
| J.Heald Coaching Ltd | Arts & recreation | 2012 |
| Jack Cardiff Associates Ltd | Administrative & support | 2017 |
| Jact Summer Schools Trust | Education | 2010 |
| JAH Bodywork Limited | Wholesale & retail | 2024 |
| JAI Consulting Ltd | Professional & scientific | 2025 |
| Jake Cole Financial Solutions Limited | Financial services | 2024 |
| JAM Medical Services Limited | Health & social care | 2019 |
| James Eade Limited | Manufacturing | 2003 |
| James Rose Ltd | Professional & scientific | 2022 |
| Jamjarjobs Limited | Administrative & support | 2007 |
| Japan Research Consultants Ltd | Administrative & support | 2021 |