| Inspyre Plus Limited | Health & social care | 2017 |
| Installpros Group Ltd | Wholesale & retail | 2023 |
| Institutional Marketing and Consulting | | 1996 |
| Insulated Limited | Construction | 2022 |
| Insulation Group UK Limited | Construction | 2026 |
| Insure Homes Limited | Financial services | 1998 |
| Insure&Invest Ltd | Professional & scientific | 2023 |
| INSURED4BUSINESS Ltd | Financial services | 2016 |
| Insurety Ltd | Financial services | 2019 |
| Insythes Limited | Professional & scientific | 2022 |
| Intagood Construction Limited | Construction | 2017 |
| Intandem Life Ltd | Wholesale & retail | 2025 |
| Integra Resources Limited | Professional & scientific | 1989 |
| Integrated International Payroll (Holdings) Ltd | Administrative & support | 2016 |
| Integrated International Payroll Limited | Information & communication | 2003 |
| Integrated Systems Events Ltd | Administrative & support | 2023 |
| Integrated Team Solutions Limited | Education | 1998 |
| Integrator Holdings Ltd | Administrative & support | 2019 |
| Integritas Contract Services Limited | Transport & logistics | 2014 |
| Integrity Flooring Ltd | Extraterritorial | 2025 |
| Intellicraft Limited | Information & communication | 2010 |
| Intelligent Data Capture Limited | Information & communication | 1996 |
| Intelligent Human Resources Limited | Wholesale & retail | 2018 |
| Intelligent Index Marketing Ltd | Professional & scientific | 2020 |
| Intelligent Venue Solutions Limited | Administrative & support | 2005 |
| Intentionality Consulting Ltd | Professional & scientific | 2012 |
| Interactive Minds Limited | Wholesale & retail | 2004 |
| Intergas Cheltenham Limited | Construction | 2012 |
| Intergen Homes Limited | Construction | 2018 |
| Intergrated Security Solutions Limited | Administrative & support | 2005 |
| Interim Project Engineering Ltd | Information & communication | 2013 |
| Interior Flooring Ltd | Construction | 1997 |
| Interlink Holdings (UK) Limited | Financial services | 2019 |
| Interlink L.G. Limited | Arts & recreation | 1995 |
| Interlink LG Investments Limited | Construction | 2021 |
| International Engineering Suppliers Ltd | Other services | 2023 |
| International Fire Consultants Limited | Professional & scientific | 1987 |
| International Food Ingredients Ltd | Financial services | 2023 |
| International Fusion Systems Ltd | Professional & scientific | 2021 |
| International Network Technologies Organization Limited | Information & communication | 1994 |
| Interos International Ltd | Information & communication | 2020 |
| Interpoint Career Services Limited | Professional & scientific | 1997 |
| Interview Performance Ltd | Professional & scientific | 2026 |
| Interx Clinic Ltd | Health & social care | 2007 |
| Inteva Productions Limited | Administrative & support | 2000 |
| Into the Wold Limited | Administrative & support | 2025 |
| Into Tomorrow Consultancy Limited | Professional & scientific | 2025 |
| Intoco Limited | Extraterritorial | 1982 |
| Inventing Itineraries Limited | Administrative & support | 2011 |
| Inverse Clothing Ltd | Manufacturing | 2025 |
| Investa Property Limited | Real estate | 2016 |
| Investa Property Ventures Ltd | Real estate | 2024 |
| Invictus Barristers Chambers Limited | Professional & scientific | 2012 |
| Invictus Build Limited | Construction | 2024 |
| Invincible Safety Limited | Professional & scientific | 1973 |
| Invu (UK) Limited | Professional & scientific | 1997 |
| Invu 2007 Limited | Information & communication | 2007 |
| Inwebdesign Ltd | Information & communication | 2024 |
| Iofoodsuk Ltd | Hospitality | 2023 |
| Iohk UK Limited | Professional & scientific | 2018 |
| Ioioi Ltd | Information & communication | 2017 |
| ION Solutions Ltd | Transport & logistics | 2026 |
| Ipipeline (TCP) Limited | Information & communication | 1987 |
| Ipipeline Limited | Information & communication | 1995 |
| Ippex Global Limited | Information & communication | 2016 |
| Ipro Phones Ltd | Wholesale & retail | 2026 |
| IQ Group Investments Limited | Education | 2016 |
| IQ Hotels Limited | Hospitality | 2012 |
| IR DNO (Employee) Limited | Financial services | 2024 |
| IR DNO Colbrans Holdco Limited | Energy | 2021 |
| IR DNO Construction Limited | Financial services | 2024 |
| IR DNO ESS Limited | Energy | 2023 |
| IR DNO Gowhole Holdco Limited | Energy | 2021 |
| IR DNO Limited | Energy | 2022 |
| IR DNO Midco II Limited | Financial services | 2024 |
| IR DNO Midco Limited | Financial services | 2024 |
| IR DNO Opco Limited | Financial services | 2024 |
| IR DNO Parkgate Holdco Limited | Financial services | 2022 |
| IR DNO Perwinnes Holdco Limited | Financial services | 2022 |
| IR Equipment Limited | Professional & scientific | 2023 |
| IR TNO (Employee) Limited | Financial services | 2023 |
| IR TNO (Midco) Limited | Financial services | 2023 |
| IR12 Limited | Energy | 2022 |
| IR14 Limited | Energy | 2022 |
| IR35 Manager Limited | Information & communication | 2021 |
| Irenicon Limited | Information & communication | 1980 |
| Iress FS Limited | Information & communication | 1994 |
| Iress Portal Limited | Information & communication | 1991 |
| Iress UK Holdings Limited | Financial services | 2013 |
| Iridium Lynx Ltd | Information & communication | 2019 |
| IRL Properties Ltd | Real estate | 2026 |
| Iron-Mills Ltd | Wholesale & retail | 2020 |
| Ironbridge Bess Limited | Energy | 2022 |
| Ironbridge Green NG Limited | Financial services | 2022 |
| Ironbridge Group Ltd | Wholesale & retail | 2025 |
| Ironforge Homes Ltd | Real estate | 2025 |
| Irongod Ltd | Wholesale & retail | 2026 |
| Ironwood Systems Limited | Information & communication | 2025 |
| Irrefutable Health Limited | Health & social care | 2015 |
| Irwell House Ltd | Real estate | 2019 |