| Indren Investments Limited | Financial services | 2021 |
| Induscourt Limited | Real estate | 1985 |
| Infinite Energy Advisory Ltd | Professional & scientific | 2020 |
| Infinity Care Limited | Health & social care | 2006 |
| Influencifymedia Ltd | Manufacturing | 2024 |
| Ingram Construction Limited | Real estate | 1983 |
| Inion Group Ltd | Wholesale & retail | 2024 |
| Inkara Ltd | Information & communication | 2025 |
| Innovative Elite Safety Training Limited | Education | 2021 |
| Innovative Sports Consultancy Limited | Arts & recreation | 2010 |
| Innovista Marketing Limited | Professional & scientific | 2025 |
| Input Joinery Holding Company Limited | Financial services | 2015 |
| Input Joinery Limited | Construction | 1979 |
| Input Windows & Conservatories Limited | Professional & scientific | 1993 |
| Insa Solutions Limited | Construction | 2021 |
| Inseto (UK) Limited | Wholesale & retail | 1987 |
| Instrupro Control Solutions Ltd | Professional & scientific | 2024 |
| Intelliinsight Limited | Information & communication | 2020 |
| Interstellar INK Limited | Real estate | 2024 |
| Inverdeen Limited | Wholesale & retail | 2014 |
| Inviting Accommodation Limited | Real estate | 2026 |
| IPM Central CIC | Education | 2022 |
| Ireland Motorsports CIC | Education | 2024 |
| Irepair Ltd | Other services | 2023 |
| Irving Sykes Interiors Ltd | Manufacturing | 2016 |
| ISI Homes Limited | Real estate | 2019 |
| Itech 49 Limited | Wholesale & retail | 2026 |
| Itech Portsmouth Limited | Wholesale & retail | 2019 |
| Itoria Ltd | Information & communication | 2026 |
| ITS the Money GUY Ltd | Professional & scientific | 2018 |
| Ivan Siska Ltd | Information & communication | 2021 |
| Ivelo Construction Ltd | Construction | 2026 |
| IVT Car Repairs Ltd | Wholesale & retail | 2022 |
| J H Newman Limited | Health & social care | 2019 |
| J Keenan Ltd | Transport & logistics | 2026 |
| J L Commercial Services Ltd | Construction | 2018 |
| J M Business Advisors Ltd | Professional & scientific | 2016 |
| J Nurseries Ltd | Education | 2024 |
| J Pollard Roofing Ltd | Construction | 2026 |
| J Stump & Co Limited | Real estate | 2025 |
| J Williams Property Ltd | Real estate | 2024 |
| J&S Trading Ltd | Wholesale & retail | 2026 |
| J&Z Homes Limited | Real estate | 2022 |
| J-Four Properties Limited | Real estate | 2021 |
| J. & J. Carter Limited | Manufacturing | 1988 |
| J. Chandler & Company, Limited | Wholesale & retail | 1925 |
| J. Mitchell Agricultural Hauliers Ltd | Transport & logistics | 2003 |
| J.Chandler & Company(Buckfast),Limited | Manufacturing | 1927 |
| J.J. LI Limited | Construction | 2003 |
| J.R. Ashworth (Plumbing & Heating) Limited | Construction | 1979 |
| J.T.Profiles Ltd | Construction | 2022 |
| J4 Premier Ltd | Administrative & support | 2023 |
| J5 Management Limited | Professional & scientific | 2025 |
| Jack's Backhaus Limited | Manufacturing | 2025 |
| Jade Plant and Machinery Ltd | Mining & quarrying | 2009 |
| Jaer Book-Keeping Limited | Professional & scientific | 2019 |
| Jakpla Transport Ltd | Transport & logistics | 2018 |
| Jalis Carpentry Limited | Construction | 2003 |
| Jamaican Kitchen Ltd | Hospitality | 2025 |
| James & David Ltd | Information & communication | 2026 |
| James Palmer Build Limited | Construction | 2022 |
| James Recycling Limited | Water & waste | 2025 |
| James' Place Adult Daycare Ltd | Health & social care | 2020 |
| Jamison Properties (Group Holdings) Limited | Construction | 1960 |
| Jams Estate Ltd | Real estate | 2018 |
| Jandawaters Ltd | Financial services | 2025 |
| Janus Learning Ltd | Education | 2025 |
| Janusz Ltd | Transport & logistics | 2012 |
| Janz Performance Ltd | Wholesale & retail | 2018 |
| Jarek Transport Ltd | Transport & logistics | 2012 |
| Jaura Group Ltd | Real estate | 2026 |
| Jayvin Systems Limited | Manufacturing | 2024 |
| Jbmc Ltd | Construction | 2018 |
| JBP Electrical Services Limited | Construction | 2020 |
| Jbph Limited | Construction | 2012 |
| Jbridger Consultancy Ltd | Information & communication | 2016 |
| JBS AGE of Empires Ltd | Construction | 2023 |
| JCW Aero Ltd | Transport & logistics | 2017 |
| JD Catering Equipment Rental Limited | Administrative & support | 2003 |
| JD Site Engineering Limited | Construction | 2013 |
| Jermayne Court (Andover) RTM Company Limited | Households | 2021 |
| JET Washing Services Ltd | Administrative & support | 2021 |
| Jewel & Crystal Solutions Limited | Health & social care | 2022 |
| Jewellery Outlook Ltd | Information & communication | 2009 |
| JHB Hire Services Limited | Transport & logistics | 2016 |
| Jimmy Trans Limited | Transport & logistics | 2014 |
| Jive Events Limited | Arts & recreation | 2015 |
| JK Studios Limited | Information & communication | 2011 |
| JL Fibre Splicing Ltd | Construction | 2018 |
| JL Project Consulting Services Limited | Information & communication | 2014 |
| JLG Digital Ltd | Information & communication | 2015 |
| Jlis and New Threads Ltd | Wholesale & retail | 2002 |
| JM FAM (UK) Limited | Wholesale & retail | 2026 |
| JMM Trading (UK) Limited | Professional & scientific | 2015 |
| JMS Fire and Security Limited | Construction | 2022 |
| Jnewitt Limited | Information & communication | 2019 |
| JO Parker Design Limited | Professional & scientific | 2019 |
| JO Winchcombe Limited | Other services | 2017 |
| Joceline House Ltd | Real estate | 2024 |
| Jocina C.I.C. | Real estate | 2023 |