| Inclusion Detection Ltd | Information & communication | 2022 |
| Independent Moving Pictures Limited | Information & communication | 2008 |
| Indestruct Ltd | Transport & logistics | 2025 |
| Indoorsy Ltd | Wholesale & retail | 2025 |
| Infinite Biomass Ltd | Energy | 2014 |
| Infinite Data Limited | Energy | 2026 |
| Infinite Pencarreg Limited | Energy | 2025 |
| Infinite Renewable Solutions Ltd | Energy | 2013 |
| Infinite Renewables Group Limited | Energy | 2015 |
| Infinite Renewables Group Services Ltd | Energy | 2018 |
| Infinite Renewables Holdings Ltd | Professional & scientific | 2024 |
| Infinite Renewables Ltd | Energy | 2010 |
| Infinite Renewables Wales Ltd | Energy | 2023 |
| Infinite Solar Ltd | Energy | 2014 |
| Infinite Ventures (Blaen Morlais) Limited | Energy | 2013 |
| Infinite Ventures (Ffyndaff) Limited | Energy | 2013 |
| Infinite Ventures (Haregrove) Limited | Energy | 2014 |
| Infinite Ventures (Llethr DDU) Limited | Energy | 2013 |
| Infinite Ventures (Shawell) Ltd | Energy | 2012 |
| Infinite Ventures (Waldrons) Ltd | Energy | 2012 |
| Infinite Ventures (Wentloog) Limited | Energy | 2013 |
| Infinity Exploration Limited | Mining & quarrying | 2017 |
| Influx Live Ltd | Arts & recreation | 2019 |
| Infoteam Group of Companies Limited | Financial services | 2025 |
| Infoteam International Limited | Administrative & support | 2019 |
| Ingenioer Verdal Limited | Extraterritorial | 2009 |
| Ingleback Limited | Administrative & support | 2018 |
| Inglelea Limited | Wholesale & retail | 2024 |
| Ingleross Limited | Wholesale & retail | 2017 |
| Ingleson Limited | Extraterritorial | 2025 |
| Ingram & Williams Ltd | Other services | 2023 |
| Initiate Architecture Ltd | Professional & scientific | 2020 |
| Initiate Projects Ltd | Real estate | 2025 |
| Inkredible Tattoo & Piercing Ltd | Arts & recreation | 2025 |
| Inndeleon Ltd | Transport & logistics | 2023 |
| Innoview International Limited | Manufacturing | 2021 |
| Inovaze Ltd | Information & communication | 2009 |
| Inscapes Holdings Limited | Financial services | 2023 |
| Inscapes Sports Limited | Manufacturing | 2013 |
| Insight Create Ltd | Manufacturing | 2025 |
| Inspirations (Internet) Ltd | Wholesale & retail | 2024 |
| Inspirations Hair LAB Ltd | Other services | 2017 |
| Inspire Design (Holdings) Limited | Professional & scientific | 2024 |
| Inspire Design Limited | Professional & scientific | 2003 |
| Inspire Drone Surveys & Inspections Ltd | Information & communication | 2019 |
| Inst. of Accessibility | Other services | 2024 |
| Intawest Limited | Extraterritorial | 2025 |
| Integrity Firestop Systems Ltd | Administrative & support | 2017 |
| Inter GAS Home Heating Limited | Wholesale & retail | 2008 |
| Intercontinental Marine Ltd | Manufacturing | 2022 |
| Interdependent Properties Ltd | Real estate | 2019 |
| International Policing Solutions Limited | Professional & scientific | 2012 |
| International Soft Drinks Ltd | Manufacturing | 2010 |
| Intracam Limited | Extraterritorial | 2024 |
| Intrakey Limited | Wholesale & retail | 2025 |
| Invacare Limited | Wholesale & retail | 2004 |
| Invacare UK Operations Limited | Health & social care | 1996 |
| Invamed Group Limited | Professional & scientific | 2000 |
| Invamed Holdings Limited | Financial services | 2025 |
| Invamed Limited | Manufacturing | 2000 |
| Invisible Walls Community Interest Company | Other services | 2023 |
| IOA Foundation Community Interest Company | Professional & scientific | 2025 |
| Ioano CYF. | Health & social care | 2026 |
| Iolis Ltd | Professional & scientific | 2019 |
| Iowp Ltd | Education | 2025 |
| IPW Distribution Ltd | Transport & logistics | 2018 |
| IQU Prompting Limited | Information & communication | 2013 |
| Iraqi Businessmen Union - "United Kingdom Branch" Limited | Other services | 2009 |
| Irate Investment Limited | Education | 2013 |
| IRB Contractors Limited | Construction | 2012 |
| Ironaxis Ltd | Mining & quarrying | 2025 |
| Irvin Aerospace Limited | Professional & scientific | 1991 |
| Irvingq Limited | Manufacturing | 1990 |
| Isaac Coaching Ltd | Education | 2026 |
| Isabella's Restaurant Limited | Hospitality | 2012 |
| Isca Bookkeeping and Accountancy Solutions Ltd | Professional & scientific | 2018 |
| Isho Global Limited | Wholesale & retail | 2026 |
| Island Cottages Holidays Limited | Hospitality | 2024 |
| Islay House Limited | Hospitality | 2014 |
| Istanbul Barbers Pyle Ltd | Other services | 2025 |
| Itchy Fish Film Limited | Information & communication | 2011 |
| Itcs (UK) Ltd. | Information & communication | 2004 |
| ITS ALL 2 Much Limited | Arts & recreation | 2010 |
| IVY Tower Village Management Limited | Real estate | 2003 |
| Izamar Ltd | Transport & logistics | 2026 |
| J & D Water Consultants Ltd | Professional & scientific | 2014 |
| J a R Engineering Ltd | Construction | 2011 |
| J C Electric Limited | Wholesale & retail | 2007 |
| J D Hever Limited | Construction | 2018 |
| J Evans Rail Site Management Ltd | Professional & scientific | 2018 |
| J M Curtis & Sons Building Company Ltd | Construction | 2025 |
| J M Vernon Properties Limited | Real estate | 2011 |
| J P David Limited | Construction | 2008 |
| J P Morgan Haulage Ltd | Transport & logistics | 2021 |
| J Robbins Property Ltd | Real estate | 2020 |
| J Smith Property Ltd | Real estate | 2018 |
| J Squared Decorating Services Limited | Construction | 2023 |
| J W Tudor Limited | Wholesale & retail | 1960 |
| J Watts Body Repairs Limited | Wholesale & retail | 2002 |
| J&A Jones Property Limited | Real estate | 2024 |