| IAN Couriers Limited | Transport & logistics | 2025 |
| ICC City Ltd | Other services | 2017 |
| Iceddelight Ltd | Wholesale & retail | 2025 |
| ICM Contractors Ltd | Construction | 2023 |
| ICO Electrical Limited | Construction | 2016 |
| Iconic Transport Ltd | Extraterritorial | 2019 |
| ICS Group Limited | Real estate | 2014 |
| ICU Fire and Security Solutions Ltd | Construction | 2020 |
| ID Graphics Limited | Other services | 2013 |
| Idsecure Limited | Extraterritorial | 2020 |
| IF Properties Limited | Real estate | 2020 |
| IF6WAS9 Design Limited | Information & communication | 2004 |
| Igloo Environmental Limited | Construction | 2009 |
| Igloo Investments Limited | Real estate | 2023 |
| IH Building Control Consultants Limited | Professional & scientific | 2012 |
| Imagine Design Install Ltd | Construction | 2019 |
| IMD Architectural Metalwork Ltd | Construction | 2021 |
| Imetal Limited | Professional & scientific | 2025 |
| Imls Coaching & Consulting Limited | Administrative & support | 2014 |
| Immy MDX Ltd | Professional & scientific | 2014 |
| Impact Arts LAB Ltd | Professional & scientific | 2023 |
| Impact Creative Limited | Arts & recreation | 2010 |
| Imperial Quality Homes Limited | Real estate | 2002 |
| Imperial Thermal Engineering Ltd | Manufacturing | 2006 |
| Imperium Assessments Limited | Administrative & support | 2019 |
| Impossible Vision Ltd | Professional & scientific | 2025 |
| Impulse Trampoline Club Ltd | Arts & recreation | 2024 |
| In-Synergy Healthcare Solutions Limited | Professional & scientific | 2015 |
| Inch Construction Limited | Construction | 2008 |
| Incus Advisory Ltd | Professional & scientific | 2026 |
| Incus Surgical Limited | Health & social care | 1988 |
| Independent People Homecare Limited | Health & social care | 2011 |
| Infinite AI Studios Ltd | Information & communication | 2026 |
| Infinity Charters Ltd | Transport & logistics | 2017 |
| Infinity Consultants and Medicare Limited | Health & social care | 2014 |
| Ingestum Ltd | Wholesale & retail | 2018 |
| Inglezo Souvlaki Co. Ltd | Hospitality | 2026 |
| Inkoperated Limited | Administrative & support | 2010 |
| Inline Motors (UK) Limited | Wholesale & retail | 2025 |
| Innova Care Limited | Health & social care | 1997 |
| Innovar Sign and Design Limited | Manufacturing | 2011 |
| Innovation Racing Ltd | Arts & recreation | 2022 |
| Innovative Business Ltd | Wholesale & retail | 2016 |
| Innovative Healing Limited | Health & social care | 2011 |
| Insignia Translations Ltd | Professional & scientific | 2022 |
| Inspired Architectural Studio Ltd | Professional & scientific | 2026 |
| Inspiring Salons Limited | Professional & scientific | 2015 |
| Instacool Limited | Energy | 2015 |
| Insuretech.Investments Ltd | Financial services | 2025 |
| Intellect Forex Limited | Financial services | 2016 |
| Intellieon Limited | Information & communication | 2013 |
| Intelligent Communications Solutions Limited | Information & communication | 2004 |
| Interconnected Search Limited | Administrative & support | 2024 |
| Internal Audit & Risk Services Ltd | Professional & scientific | 2007 |
| International Safety and Survival Equipment Technical Association Ltd. | Professional & scientific | 1973 |
| Introdawn Limited | Professional & scientific | 1987 |
| Investitude Limited | Real estate | 2026 |
| Investquest Limited | Information & communication | 2018 |
| Invictus Aesthetics Ltd | Health & social care | 2022 |
| Inzanius Ltd | Information & communication | 2022 |
| Iriss Ltd | Professional & scientific | 2008 |
| Iron View Management Company Limited | Households | 2006 |
| Irontown Accommodation Ltd | Hospitality | 2024 |
| Irontown Beverage Ltd | Hospitality | 2024 |
| Irontown Development Ltd | Construction | 2024 |
| Ironwright of Dunmow Ltd. | Manufacturing | 2016 |
| Isaac FOX Ltd | Real estate | 2023 |
| Isedale WA C.I.C. | Education | 2018 |
| Island Advertising Limited | Other services | 1995 |
| It's Lolly Limited | Information & communication | 2009 |
| It's Safe Limited | Professional & scientific | 2014 |
| Itsgivingglobal Ltd | Administrative & support | 2026 |
| IVY245 Limited | Real estate | 2026 |
| IWK Limited | Real estate | 2001 |
| IWORK247 Limited | Professional & scientific | 2022 |
| J & E Hauliers Ltd | Agriculture & fishing | 2026 |
| J & J Design & Build Ltd | Construction | 2024 |
| J & M Hills Contractors Limited | Construction | 2018 |
| J & R Scaffolding Services Limited | Construction | 2018 |
| J & S Wells Ltd | Administrative & support | 2024 |
| J & Y Motors Ltd | Wholesale & retail | 2024 |
| J and J General Builders Ltd | Construction | 2015 |
| J and R Roofing and Construction Ltd | Construction | 2025 |
| J B J Holdings Limited | Professional & scientific | 1975 |
| J B J Pallets Limited | Manufacturing | 2000 |
| J C Coetzee Ltd | Manufacturing | 2021 |
| J Ferguson Products Ltd | Extraterritorial | 2026 |
| J M Jewels Limited | Wholesale & retail | 2026 |
| J Nash Trading Limited | Real estate | 2017 |
| J R Crayston & Sons Limited | Agriculture & fishing | 2008 |
| J Verité Limited | Wholesale & retail | 2025 |
| J W Construction & Padel Courts Ltd | Construction | 2026 |
| J W Machinery Services Limited | Manufacturing | 2004 |
| J&J Maintenance Solutions Ltd | Professional & scientific | 2021 |
| J&L Alarms Limited | Administrative & support | 2013 |
| J&R Services (Essex) Ltd | Energy | 2017 |
| J&S Tillotson Limited | Administrative & support | 2012 |
| J&T Creations Ltd. | Manufacturing | 2014 |
| J'Adore Electrics & Air Conditioning Ltd | Manufacturing | 2021 |
| J'S Laboratory Ltd | Health & social care | 2016 |