| Inkaza Ltd | Real estate | 2024 |
| Inkfold Studio Ltd | Information & communication | 2025 |
| Inn Quests Limited | Hospitality | 1984 |
| Inner Town Homes Limited | Real estate | 1962 |
| Innon Energy Ltd. | Information & communication | 2008 |
| Innovatify Ltd | Information & communication | 2022 |
| Innovation DB and Forum Limited | Information & communication | 2009 |
| Innovation Sports Limited | Arts & recreation | 2004 |
| Innovix Advisory Ltd | Information & communication | 2024 |
| INS Business Ltd | Wholesale & retail | 2016 |
| INS4 Consulting Limited | Information & communication | 2023 |
| INS4 Limited | Information & communication | 2023 |
| Insci Solutions Limited | Professional & scientific | 2025 |
| Inserval Global Brokers Limited | Financial services | 2007 |
| INSIGHT2IMPLEMENTATION Limited | Administrative & support | 2005 |
| Inspiring Workplaces Group Limited | Professional & scientific | 2013 |
| Insta Care One Ltd | Health & social care | 2022 |
| Installations Services Limited | Construction | 2008 |
| Instant Coffee Supplies Limited | Wholesale & retail | 2011 |
| Intaellisys Limited | Professional & scientific | 2026 |
| Intec Plumbing & Heating Ltd | Construction | 2009 |
| Integrated Consultancy Limited | Construction | 2019 |
| Integrated Systems Installations Limited | Other services | 1994 |
| Intellicapita Limited | Extraterritorial | 2014 |
| Intelligent Choice Limited | Financial services | 2000 |
| Intellisolutions Limited | Information & communication | 2015 |
| Interexpansion Ltd | Public administration | 2025 |
| Interfaith in Action | Other services | 2011 |
| Interfractional Business Services Limited | Professional & scientific | 2024 |
| Interglobe Ventures Ltd | Wholesale & retail | 2015 |
| Interimcio Limited | Information & communication | 2025 |
| Intermede Vacances (Sales) Limited | Wholesale & retail | 2003 |
| International Capital Market Services Association | Other services | 2014 |
| International Merchandising Services Ltd | Information & communication | 2019 |
| International Shinto Foundation Limited | Other services | 2001 |
| Interorganised Ltd | Professional & scientific | 2024 |
| Intertime Services Ltd | Information & communication | 2012 |
| Interviewer Quality Control Scheme(The) | Professional & scientific | 1986 |
| Into the Loft Limited | Construction | 2011 |
| Intothebuild / Intotheloft Limited | Construction | 2026 |
| Invest Loch Ltd | Extraterritorial | 2025 |
| Investas Property Limited | Real estate | 2017 |
| Investlink Consulting Ltd | Information & communication | 2025 |
| Investment Solutions Strategy Consultants Ltd | Professional & scientific | 2014 |
| Io-Transform Ltd | Professional & scientific | 2021 |
| Ioannouproperties Ltd | Households | 2025 |
| Iotalent Group Ltd | Information & communication | 2025 |
| Iotb Limited | Hospitality | 2025 |
| Iplumb & Heat Ltd | Construction | 2012 |
| IPR Futures Limited | Information & communication | 2016 |
| IRA Software Solutions Limited | Information & communication | 2011 |
| Iridium Creative Limited | Professional & scientific | 2024 |
| Iris Amaze Limited | Information & communication | 2013 |
| Iris Commerce Ltd | Wholesale & retail | 2025 |
| Iris UK Partners Limited | Professional & scientific | 2015 |
| Irnity Corporate Solutions Limited | Information & communication | 2025 |
| Iron POT Limited | Hospitality | 2016 |
| Iron Ronin Ltd | Professional & scientific | 2022 |
| Iron Sights Ltd | Administrative & support | 2014 |
| Isabel's Laundry Ltd | Administrative & support | 2023 |
| Isabella MAY Studios Limited | Education | 2026 |
| ISC Estates Limited | Construction | 1996 |
| ISC Leasing (Ipswich) Limited | Health & social care | 1996 |
| ISC Projects Limited | Health & social care | 1996 |
| Iscience Solutions Limited | Manufacturing | 2024 |
| Iseo Capital Limited | Real estate | 2024 |
| Isikli Limited | Hospitality | 2023 |
| Islecliff Property Management Company Limited | Real estate | 1991 |
| Isme Ltd | Real estate | 2023 |
| Isosceles Limited | Professional & scientific | 2011 |
| ISP Trading Ltd | Wholesale & retail | 2016 |
| Isps Power of Sports Fund | Other services | 2011 |
| ISU International Limited | Wholesale & retail | 2023 |
| IT Manipals Limited | Information & communication | 2015 |
| It-Unique Solutions Limited | Information & communication | 2007 |
| Itar Limited | Manufacturing | 2015 |
| Itenergy Limited | Wholesale & retail | 1998 |
| Ithaca Partners Limited | Professional & scientific | 2007 |
| Itpa Construction Ltd | Construction | 2026 |
| ITS (Surrey) Limited | Information & communication | 2007 |
| Itzasecret Limited | Extraterritorial | 2021 |
| Iuna Investments Limited | Real estate | 2025 |
| Ivan Thomas (Coachworks) Ltd | Wholesale & retail | 2012 |
| Ivantage Limited | Professional & scientific | 2013 |
| IVY & Bell Ltd | Wholesale & retail | 2022 |
| Izimali Ltd | Professional & scientific | 2007 |
| J & B Baker Services Ltd | Wholesale & retail | 2019 |
| J & S Benton Ltd | Health & social care | 2006 |
| J & S Electrical Solutions LLP | | 2024 |
| J and C Bookkeeping Services Ltd | Professional & scientific | 2023 |
| J and J Gibson Limited | Real estate | 2021 |
| J B ROY Properties Ltd | Real estate | 2018 |
| J D Motorsport Limited | Wholesale & retail | 2006 |
| J Frost Civils Ltd | Construction | 2023 |
| J Gallagher Physiotherapy Limited | Health & social care | 2021 |
| J Giddings Property Rental Limited | Real estate | 2019 |
| J Judge Medical Services Ltd | Health & social care | 2021 |
| J Lawrence Joinery Limited | Manufacturing | 2026 |
| J Marsh Roof&Build Ltd | Construction | 2025 |
| J Neaves Property Management Limited | Real estate | 2021 |