| IN THA CUT Worldwide Limited | Wholesale & retail | 2023 |
| Independence With Dignity Support Services Ltd | Health & social care | 2012 |
| Indul Ltd | Manufacturing | 2022 |
| Infast Fire Protection Limited | Professional & scientific | 2020 |
| Infinatelayers Limited | Manufacturing | 2024 |
| Ink-Credible Tattoo Ltd | Hospitality | 2022 |
| Insphire Limited | Information & communication | 1997 |
| Intelligent Design Homes (Cumnor) Limited | Extraterritorial | 2016 |
| Intelligent Design Homes Limited | Construction | 2011 |
| Intelligent Horsemanship Limited | Education | 2002 |
| International OT Solutions Ltd | Professional & scientific | 2024 |
| Intex Property Solutions Ltd | Construction | 2015 |
| IO Capital Limited | Professional & scientific | 2021 |
| IPC Windows and Plastics Limited | Construction | 2003 |
| IPC Windows Holdings Ltd | Financial services | 2023 |
| Ishtar Bidco Limited | Financial services | 2018 |
| Ishtar Midco Limited | Financial services | 2018 |
| Ishtar Topco Limited | Financial services | 2018 |
| J & B Marketing Limited | Professional & scientific | 2025 |
| J & B Services Ltd. | Wholesale & retail | 1999 |
| J & D Developments Limited | Construction | 2003 |
| J & P Store Ltd | Wholesale & retail | 2019 |
| J & R Houses Limited | Real estate | 2024 |
| J. Simmonds-Hugo Limited | Administrative & support | 1996 |
| Jacquet Weston Enterprises Limited | Manufacturing | 2009 |
| Jacquet Weston Limited | Manufacturing | 2000 |
| Jade Vans Limited | Financial services | 2022 |
| JAG Products Ltd | Administrative & support | 2008 |
| JAI Composites Limited | Professional & scientific | 2023 |
| Jake Fielder Limited | Construction | 2003 |
| James Coyle Management Ltd | Professional & scientific | 2025 |
| James Walker (Building Contractors) Limited | Construction | 2004 |
| Jamie Osborne Racing Limited | Arts & recreation | 2026 |
| Jannaway Freelancing Ltd | Professional & scientific | 2023 |
| Jasper Leadbeater Art Ltd | Arts & recreation | 2024 |
| JC Restaurants Limited | Hospitality | 2025 |
| JCB Building (Oxfordshire) Limited | Construction | 2023 |
| Jeans & Co. Advisory Ltd | Professional & scientific | 2025 |
| Jenc Marketing Limited | Professional & scientific | 2025 |
| Jenkins Business Consulting Ltd | Professional & scientific | 2024 |
| Jens Tutoring Limited | Education | 2026 |
| Jetset Coffee Ltd | Hospitality | 2026 |
| JHD Construction Limited | Construction | 2025 |
| JM Custom Craftsman Ltd | Construction | 2026 |
| Jmbuk Consultancy Services Ltd | Information & communication | 2013 |
| Jobson Property Renovations Limited | Construction | 2025 |
| Jobson Renovations Ltd | Construction | 2016 |
| JOE Dickinson Music Limited | Arts & recreation | 2018 |
| John Day Engineering (Welford) Limited | Wholesale & retail | 1984 |
| John Gale Limited | Agriculture & fishing | 1958 |
| John Hughes Racehorse Transport Limited | Transport & logistics | 2003 |
| John Vetch House Ltd | Real estate | 2015 |
| John's Tea Room Ltd | Hospitality | 2026 |
| JON Shatford Consulting Ltd | Professional & scientific | 2020 |
| JON Shatford Limited | Administrative & support | 2018 |
| Julian Turner Garden Services Ltd | Administrative & support | 2017 |
| Julian Turner Limited | Administrative & support | 2003 |
| Jurassic Holdings Limited | Financial services | 2021 |
| JWB Inventory Services Ltd | Other services | 2008 |
| K & G Gibbard Construction Limited | Construction | 2003 |
| K and C Services Ltd | Construction | 2026 |
| Kahlenberg UK Limited | Wholesale & retail | 2011 |
| Kain Cook Ltd | Hospitality | 2025 |
| Kale Interiors Ltd | Construction | 2024 |
| Kate Sirrell Limited | Professional & scientific | 1996 |
| Katie O'Sullivan Art Limited | Arts & recreation | 2026 |
| Katier Ltd | Administrative & support | 2011 |
| KCD Holdings Limited | Construction | 2016 |
| KCS Automotive Ltd | Information & communication | 2020 |
| Kearnsco Limited | Information & communication | 2016 |
| Keen Plumbers Ltd | Construction | 2024 |
| Kelcon Capital Limited | Hospitality | 2025 |
| Kelex Labs Ltd | Information & communication | 2015 |
| Kelk Consulting & Services Ltd | Information & communication | 2007 |
| KEN Gamble International Horse Transport Limited | Transport & logistics | 2003 |
| Kennet District Gymnastic Centre Limited | Arts & recreation | 2011 |
| Kennet Electrics Ltd | Construction | 2017 |
| Kennet Holdings (Swindon) Ltd | Professional & scientific | 2017 |
| Kennet Holdings Limited | Professional & scientific | 2004 |
| Kennet Roofing Limited | Construction | 1983 |
| Kerridge Commercial Systems (Bidco) Limited | Financial services | 2014 |
| Kerridge Commercial Systems (KSH) Limited | Information & communication | 1965 |
| Kerridge Commercial Systems (Midco) Limited | Financial services | 2015 |
| Kerridge Commercial Systems Limited | Information & communication | 2009 |
| Kerridge Commercial Systems Trustee Company Limited | Professional & scientific | 2010 |
| Kerridge Properties Limited | Real estate | 1997 |
| Keytoll Capital Limited | Hospitality | 2025 |
| Killyon Investments Limited | Real estate | 2015 |
| Kiln Dried Firewood Limited | Manufacturing | 2023 |
| Kingwood Stud Management Company Limited | Agriculture & fishing | 2010 |
| Kintbury Eco Centre CIC | Education | 2025 |
| Kintbury Remembered | Information & communication | 2022 |
| Kintulavig Housing Ltd | Construction | 2019 |
| KLC Property Development Ltd | Real estate | 2018 |
| Klipboard Group Limited | Financial services | 2014 |
| Klipboard Limited | Information & communication | 2015 |
| KPL Holdings Ltd | Financial services | 2016 |
| KPL Phase 2 Limited | Real estate | 2015 |
| KRG Southampton Limited | Hospitality | 2024 |
| Kubler Racing Ltd | Agriculture & fishing | 2011 |