| International Mission to Jewish People | Other services | 1976 |
| International Publishing Associates Limited | Professional & scientific | 1992 |
| Intertrade Wholesale Limited | Wholesale & retail | 2002 |
| Intus Biosciences UK Limited | Health & social care | 2022 |
| Invenire Risk Limited | Information & communication | 2026 |
| Inventory Management Europe Limited | Wholesale & retail | 2009 |
| INVIGOR8 Consultants Limited | Administrative & support | 2019 |
| Ioanna Sofia & Associates Ltd | Professional & scientific | 2021 |
| IOT Access Ltd | Financial services | 2025 |
| Iotie Connect Ltd | Real estate | 2022 |
| Ipgenix Limited | Professional & scientific | 2023 |
| Ironside Capital Limited | Professional & scientific | 2026 |
| Ironwood Structural Design Limited | Professional & scientific | 2010 |
| Irrepressible Limited | Information & communication | 2004 |
| Isis Windows Limited | Construction | 2006 |
| Island Wide Maintenance Ltd | Construction | 2023 |
| Itbg Consulting LLP | | 2003 |
| Itech Oxford Limited | Information & communication | 2022 |
| Itplus-Oxford Ltd | Other services | 2025 |
| Izzo Design Limited | Professional & scientific | 2012 |
| Izzy B Co Ltd | Wholesale & retail | 2018 |
| J & a Education Limited | Education | 2011 |
| J & M Property Renovations & Maintenance Ltd | Construction | 2024 |
| J a Brooks Plastering Limited | Construction | 2018 |
| J a Shirley Building Services Limited | Construction | 2003 |
| J Brown Groundwork and Plant Hire Ltd | Construction | 2023 |
| J Commerce Group Limited | Wholesale & retail | 2023 |
| J D J Holdings Limited | Financial services | 2022 |
| J D Price Consulting Limited | Professional & scientific | 2002 |
| J Fadez Ltd | Other services | 2024 |
| J H Professional Golf Services Ltd | Arts & recreation | 2013 |
| J H Textiles Limited | Wholesale & retail | 2021 |
| J Millin & SON Limited | Wholesale & retail | 2005 |
| J Palka Ltd | Wholesale & retail | 2020 |
| J R Hatton Plumbing & Heating Limited | Construction | 2013 |
| J S Parsons Consulting Limited | Professional & scientific | 2024 |
| J Whittington Logistics Limited | Professional & scientific | 2005 |
| J&J 88 Limited | Hospitality | 2026 |
| J'S Enterprises Services Ltd | Administrative & support | 2022 |
| J.E.L. Developments Limited | Construction | 2002 |
| J.Livingstone Building and Landscaping Ltd | Construction | 2022 |
| J.Otwell Developments Ltd | Construction | 2019 |
| J.S Capel Chambers (UK) Ltd | Professional & scientific | 2013 |
| J.S. Motor Services Ltd | Wholesale & retail | 2006 |
| Jack Alexander Design Ltd | Construction | 2016 |
| Jack Clifton Joinery Ltd | Manufacturing | 2019 |
| Jack James Homes Limited | Construction | 2010 |
| Jack Warner Wealth Management Limited | Financial services | 2017 |
| Jackie Grier Courage Into Clarity Limited | Professional & scientific | 2026 |
| Jackson's of Clanfield Limited | Construction | 2015 |
| Jacob Research Ltd | Administrative & support | 2017 |
| Jags Transport Ltd | Transport & logistics | 2026 |
| JAI Shankar Ltd | Health & social care | 2014 |
| Jaimee Bonassisa Mortgage Solutions Ltd | Financial services | 2017 |
| Jake Linzey Puppetry Limited | Professional & scientific | 2018 |
| Jakl Limited | Professional & scientific | 2025 |
| JAM Business Solutions Ltd | Professional & scientific | 2016 |
| James & Huan Ltd | Real estate | 2023 |
| James Bason Wealth Management Limited | Financial services | 2019 |
| James Pritchett Ltd | Construction | 2018 |
| Jamesfrench.Com Ltd. | Wholesale & retail | 2001 |
| Jameson Projects Ltd | Construction | 2015 |
| Jamesons Capital Limited | Administrative & support | 2013 |
| Jamesons Holdings Limited | Financial services | 2022 |
| Jamesons Limited | Professional & scientific | 2001 |
| Jani's Hand Car Wash Limited | Other services | 2012 |
| Jani's Property Company Limited | Real estate | 2017 |
| Japanese Engineering Services Ltd | Wholesale & retail | 2014 |
| Jarman Associates Limited | Professional & scientific | 2006 |
| Jarn Structures Limited | Professional & scientific | 2022 |
| Jason Hydraulics Limited | Manufacturing | 1999 |
| Jason Strong Builders Limited | Construction | 2011 |
| Jaunty Shopper Ltd | Wholesale & retail | 2010 |
| JB Architectural Design Ltd | Professional & scientific | 2024 |
| JB Flexible Workspace Consultant Ltd | Administrative & support | 2007 |
| JB Nails and Beauty Ltd | Other services | 2020 |
| JB Translation Services Ltd | Administrative & support | 2007 |
| JB1PUTT Limited | Extraterritorial | 2017 |
| JB1PUTT Property Limited | Real estate | 2017 |
| JBE Events Limited | Administrative & support | 2009 |
| JBM Patios & Landscaping Limited | Administrative & support | 2024 |
| JBP Solutions Limited | Professional & scientific | 2023 |
| JC Building Solutions Limited | Construction | 2007 |
| JD Ground Care Ltd | Administrative & support | 2024 |
| JD7 Quality Consulting Ltd | Professional & scientific | 2014 |
| Jeeves & Jericho Limited | Manufacturing | 2026 |
| Jeeves & Jericho the Jolly Good Tea Company Ltd | Wholesale & retail | 2010 |
| Jeffrica Limited | Financial services | 2006 |
| Jeremy Price Chartered Surveyors Limited | Professional & scientific | 2008 |
| Jessett and Pollard, the Oxfordshire Decorators Ltd | Construction | 2020 |
| Jessie's Art Shed Ltd | Education | 2017 |
| Jessplug Ltd | Hospitality | 2025 |
| JET Connections Limited | Transport & logistics | 2004 |
| Jeti Properties Ltd | Real estate | 2018 |
| JEZ Stockdale Ltd | Professional & scientific | 2023 |
| Jezjam Studios Ltd | Information & communication | 2015 |
| Jfdi Design Limited | Professional & scientific | 2021 |
| JFM Cleaning Services Limited | Administrative & support | 2008 |
| JGP Partners Ltd | Administrative & support | 2020 |
| JGP Planning Limited | Real estate | 2021 |