| IMF (It's My Funeral) Ltd | Other services | 2025 |
| IMO Property Limited | Households | 2026 |
| Impart X Limited | Administrative & support | 2022 |
| Impressions Caterers Ltd | Hospitality | 2011 |
| Inaya Estates Ltd | Real estate | 2025 |
| Inde-Tech UK Limited | Wholesale & retail | 2005 |
| Independent Personal Trainer Alliance Ltd | Education | 2020 |
| Industrial Digital Technologies Limited | Wholesale & retail | 2019 |
| Infinitx Tech Limited | Extraterritorial | 2024 |
| Infinity Sports Group Ltd | Extraterritorial | 2021 |
| Infinity Sports Management Limited | Other services | 2012 |
| Init Racing Ltd | Manufacturing | 2021 |
| Innohealth Limited | Information & communication | 2017 |
| Innsite UK Ltd | Construction | 2004 |
| Inspire Change Limited | Professional & scientific | 1999 |
| Inspired Collaboration Group Limited | Professional & scientific | 2016 |
| Inspired Design and Print Solutions Ltd | Manufacturing | 2009 |
| Intamac Systems Limited | Information & communication | 2000 |
| Integral Flooring Solutions Ltd | Construction | 2022 |
| Integral Powertrain Technology Limited | Professional & scientific | 2011 |
| Intelistrike Ltd | Information & communication | 2023 |
| Intellistall Ltd | Wholesale & retail | 2019 |
| Inter-Circuit Holdings Ltd | Financial services | 2014 |
| Interior Life Limited | Construction | 2005 |
| International Apparel Limited | Wholesale & retail | 2009 |
| Intuitas Technologies Limited | Information & communication | 2023 |
| Invigorate Development Ltd | Administrative & support | 2020 |
| Ioniq Skincare UK Limited | Wholesale & retail | 1978 |
| IOT Distribution Ltd | Wholesale & retail | 2023 |
| Ironrock Civils & Groundworks Ltd | Construction | 2026 |
| Isdera UK Ltd | Manufacturing | 2025 |
| ISM Partnerships Limited | Professional & scientific | 2019 |
| ISS (COV) Ltd | Arts & recreation | 2010 |
| ISS (MK) Ltd | Arts & recreation | 2009 |
| Isthatlevel Ltd | Construction | 2008 |
| IT at Work Ltd | Information & communication | 2007 |
| IT Does ... Limited | Extraterritorial | 2016 |
| IT Does Lighting Limited | Professional & scientific | 2004 |
| It-Mk Limited | Information & communication | 2009 |
| J Exley Engineering Limited | Wholesale & retail | 2010 |
| J Garton Limited | Real estate | 2013 |
| J Motion Limited | Information & communication | 2002 |
| J&J Automotive Media Ltd | Wholesale & retail | 2021 |
| J. Cunningham Ltd | Construction | 2022 |
| J.S Test Systems Ltd | Professional & scientific | 2024 |
| JA Gallagher Services Limited | Construction | 2025 |
| Jack's Hill Estate Limited | Real estate | 1970 |
| Jacks Hill 1955 Limited | Transport & logistics | 2026 |
| Jacks Hill Estate Towcester Ltd | Financial services | 2024 |
| Jackson Pyne Ltd. | Real estate | 2002 |
| Jacob Ward Fitness Ltd | Wholesale & retail | 2022 |
| JAE & DME Properties Limited | Real estate | 2014 |
| Jald Developments Limited | Transport & logistics | 2021 |
| James Martindale Consultancy LLP | | 2018 |
| James MOY Photography Ltd | Professional & scientific | 2012 |
| James Slade Ltd | Real estate | 2026 |
| Jamsco Limited | Construction | 2013 |
| Janson Real Estate Limited | Real estate | 2018 |
| Jayden Transport UK Limited | Transport & logistics | 2012 |
| JB Fences Ltd | Administrative & support | 2024 |
| JC Botox Ltd | Other services | 2025 |
| JC Renting Ltd | Real estate | 2020 |
| Jcdm Consulting Services Ltd | Professional & scientific | 2025 |
| JCP Consultancy Services Ltd | Professional & scientific | 2021 |
| Jctc Ltd | Other services | 2018 |
| Jeet Top Shop Ltd | Wholesale & retail | 2020 |
| Jeeves Contracting Ltd | Construction | 2009 |
| Jelley Consulting Ltd | Information & communication | 2011 |
| Jemm Property Services Limited | Real estate | 2016 |
| Jenkinson Safety Limited | Professional & scientific | 2021 |
| Jerome Harlington Limited | Professional & scientific | 2014 |
| Jessica Hayward Ltd | Real estate | 2024 |
| Jetsportuk Ltd | Manufacturing | 2023 |
| Jevatech Limited | Professional & scientific | 2018 |
| JFG Park Services Ltd | Construction | 2015 |
| JIM & Jess Property Company Limited | Real estate | 2019 |
| JJP Accounting Ltd | Professional & scientific | 2017 |
| JL (Liverpool) Regeneration LLP | | 2013 |
| JLH Investments Limited | Real estate | 2020 |
| JMC Marketing Services Ltd | Other services | 2019 |
| JMG Cooling Services Limited | Construction | 2024 |
| JMI Investments Limited | Real estate | 2006 |
| JN Installations Ltd | Construction | 2025 |
| Jo's Coffee Bars Ltd | Hospitality | 2024 |
| Jobsined Ltd | Administrative & support | 2024 |
| Joe's Automotive Ltd | Wholesale & retail | 2010 |
| Joel Mccormick Limited | Professional & scientific | 2020 |
| John Aprahamian & Company Ltd | Agriculture & fishing | 2004 |
| Jolly BAO Limited | Wholesale & retail | 2025 |
| Jonathan Humbert Ltd | Wholesale & retail | 2017 |
| Josh Mitchell Ltd | Information & communication | 2016 |
| Jrdb Limited | Financial services | 2013 |
| JSF Enterprises Ltd | Administrative & support | 2022 |
| JST Electrical Limited | Construction | 2026 |
| Jubjav Takeaways Ltd | Hospitality | 2024 |
| Jules Murphy Financial Planning Limited | Professional & scientific | 2008 |
| Julie Mills Properties Ltd | Hospitality | 2025 |
| Jwmc Blends Ltd | Wholesale & retail | 2024 |
| Jwmc Group Ltd | Wholesale & retail | 2024 |
| K Bibi Properties Limited | Construction | 2015 |