| Hybrid Mechanical Services Ltd | Construction | 2025 |
| Hydra Film Services Limited | Information & communication | 2022 |
| Hydrotec Plumbing and Heating Ltd | Construction | 2020 |
| I Love Motion Limited | Professional & scientific | 2017 |
| I R Cook Limited | Construction | 2018 |
| I-Kew Construction Ltd | Construction | 2017 |
| I-Kew Off-Site Limited | Manufacturing | 2020 |
| IAN Penny I.R.P. Limited | Information & communication | 2003 |
| Ibly Limited | Information & communication | 2024 |
| Ican Developments Limited | Real estate | 2024 |
| Iconic Commercials Limited | Wholesale & retail | 2017 |
| Ideal Hydro Ltd | Wholesale & retail | 2015 |
| Ideal Paper Company Ltd | Wholesale & retail | 2023 |
| IDM Building Solutions Ltd | Construction | 2012 |
| IDM Windows and Doors Ltd | Construction | 2012 |
| Ifzah Investments Limited | Financial services | 2021 |
| Ignite Active Fitness Limited | Arts & recreation | 2022 |
| IGW Holding Limited | Professional & scientific | 2018 |
| Ihayo Ltd | Wholesale & retail | 2023 |
| Ilexgroup Ltd | Administrative & support | 2026 |
| Illegal Eagles Ltd | Extraterritorial | 2019 |
| Illumiharli Productions Limited | Information & communication | 2024 |
| IM a Plumber Ltd | Construction | 2025 |
| Image Optics Components Limited | Manufacturing | 1986 |
| Image Optics Limited | Wholesale & retail | 1986 |
| Imar Property Ltd | Construction | 2024 |
| Impact Building and Roofing Ltd | Construction | 2019 |
| Imperial Connect Limited | Administrative & support | 2019 |
| Imperial Devices Ltd | Wholesale & retail | 2024 |
| Imperial Incorporated Ltd | Administrative & support | 2017 |
| Impetus Engineering Limited | Professional & scientific | 2015 |
| Impression Film & Video Limited | Information & communication | 2020 |
| Impressions 110 Ltd | Information & communication | 2011 |
| IN5 Broadcast Facilities Limited | Information & communication | 2004 |
| Inbellished Ltd | Manufacturing | 2023 |
| Incredibly Limited | Professional & scientific | 2011 |
| Indra Retail Ltd | Wholesale & retail | 2021 |
| Induce Design Limited | Professional & scientific | 2016 |
| Inertia Studios Ltd | Information & communication | 2016 |
| Infinite 22 Ltd | Professional & scientific | 2020 |
| Infinite Network Solutions Limited | Information & communication | 2013 |
| Infinite RB Investments Ltd | Real estate | 2023 |
| Infinity Circus Ltd | Arts & recreation | 2021 |
| Infinity PM Solutions Limited | Hospitality | 2016 |
| Infonettech Ltd | Information & communication | 2025 |
| Inframe Interiors Limited | Construction | 2014 |
| Inhouse Audio Ltd | Other services | 2019 |
| INK & Trouble Ltd | Information & communication | 2023 |
| Inked Electrical Contractors Ltd | Construction | 2025 |
| Innovate Facilities Solutions Limited | Professional & scientific | 2010 |
| Inscripture Ltd | Manufacturing | 2018 |
| Insect Research Solutions Ltd | Professional & scientific | 2021 |
| Inside OUT Records Limited | Arts & recreation | 2013 |
| Inspired Exchange Ltd | Professional & scientific | 2012 |
| Instant Living Space Ltd | Construction | 2012 |
| Integral Action Limited | Education | 2023 |
| Integral Environmental Solutions Limited | Construction | 2016 |
| Integrated Support Services Ltd | Health & social care | 2022 |
| Intelligent-Placements Ltd | Administrative & support | 2021 |
| Inter Euro Telecoms Limited | Real estate | 2010 |
| Intercept Networks Ltd | Information & communication | 2023 |
| Interec Consulting Ltd | Administrative & support | 2008 |
| International Treasury Services (Africa) Ltd | Financial services | 2011 |
| Internet Pipelines UK Ltd | Information & communication | 2011 |
| Interweb Lettings Limited | Real estate | 2025 |
| IQ Fitness Ltd | Arts & recreation | 2015 |
| Iron Lady Ltd | Other services | 2013 |
| Isaac Samuel Consulting Ltd | Administrative & support | 2024 |
| ISF Investments Limited | Real estate | 2013 |
| Isfa Technology Ltd | Information & communication | 2025 |
| Island Cooling Ltd | Energy | 2022 |
| Island Storage Ltd | Other services | 2023 |
| Istanbul Kebab (Benfleet) Limited | Hospitality | 2023 |
| IT HUT Limited | Wholesale & retail | 2016 |
| It's in Property Ltd | Real estate | 2022 |
| IT2WEB Limited | Information & communication | 1999 |
| Italian Suit Trading Company Limited | Wholesale & retail | 1998 |
| Itharta Limited | Administrative & support | 2015 |
| ITL Golf UK Ltd | Wholesale & retail | 2025 |
| Itow Ltd | Wholesale & retail | 2023 |
| Ittechera Ltd | Information & communication | 2026 |
| Ivey Investments Ltd | Real estate | 2025 |
| IVY Neary Golf Limited | Arts & recreation | 2024 |
| Iznik Limited | Hospitality | 2022 |
| J & a Fire Solutions Limited | Administrative & support | 2013 |
| J & a Fitness Ltd | Arts & recreation | 2024 |
| J & C Contractors (UK) Limited | Administrative & support | 2005 |
| J & D Food Distributors Ltd | Wholesale & retail | 1998 |
| J & M Services Essex Ltd | Construction | 2025 |
| J and M Pallet Services Limited | Wholesale & retail | 2012 |
| J Bond Carpentry and Decorating Limited | Construction | 2017 |
| J Buckingham Interiors Limited | Construction | 2022 |
| J Burton Electrical Ltd | Construction | 2020 |
| J Burton Properties Ltd | Real estate | 2020 |
| J Cooper Plastering & Rendering Limited | Other services | 2002 |
| J D L Property Company (Essex) Limited | Real estate | 2024 |
| J D Maintenance (Essex) Ltd | Construction | 2024 |
| J Daynes Decorative Finishers Ltd | Construction | 2015 |
| J Install Ltd | Other services | 2022 |
| J K L Kitchens Limited | Construction | 2006 |