| Ivinghoe Turf Limited | Administrative & support | 2007 |
| IVY Nails & Spa Ltd | Other services | 2026 |
| Izzy Taylor Eventing Ltd | Arts & recreation | 2020 |
| J & J Roofing & Building Co. Limited | Construction | 1998 |
| J & L Marquees Limited | Administrative & support | 2022 |
| J & R Homes Limited | Construction | 2015 |
| J and a Agriculture Ltd | Agriculture & fishing | 2023 |
| J B H Services Limited | Professional & scientific | 2021 |
| J C Consulting (Fmcg) Limited | Hospitality | 2018 |
| J E Miller Engineering Ltd | Manufacturing | 2012 |
| J Easton Engineering Ltd | Professional & scientific | 2016 |
| J F Polo Ltd | Arts & recreation | 2021 |
| J H Concepts Ltd | Professional & scientific | 2023 |
| J J Arbuckle Building Ltd | Construction | 2017 |
| J Moss Digger Hire Limited | Administrative & support | 2014 |
| J Smith Plumbing and Heating Limited | Construction | 2018 |
| J Tech Carpentry Ltd | Manufacturing | 2018 |
| J&E Decorating Ltd | Construction | 2025 |
| J&J Master Thatchers & Roofers Ltd | Construction | 2022 |
| J&J Property Wealth Investments Ltd | Real estate | 2025 |
| J&W Accommodations Ltd | Hospitality | 2024 |
| J-Jens Properties Ltd | Real estate | 2025 |
| J. H. Preston Ltd | Information & communication | 2022 |
| J.C. Williams Hospitality Ltd | Hospitality | 2024 |
| J.P. Belmar Limited | Professional & scientific | 2025 |
| Jabkins Ltd | Transport & logistics | 2012 |
| Jachin Group Ltd | Real estate | 2021 |
| Jachin Ltd | Real estate | 2021 |
| Jackson Builders Ltd | Construction | 2024 |
| Jackson Building Solutions Ltd | Construction | 2015 |
| Jacqui OOO Ltd | Information & communication | 2023 |
| Jacrafts Ltd | Wholesale & retail | 2024 |
| Jade Fine Dining Ltd | Hospitality | 2025 |
| Jaden's Care Options Ltd | Health & social care | 2015 |
| Jagaptiya Limited | Real estate | 2026 |
| Jakeman Lease Limited | Administrative & support | 2018 |
| James Darcy Consulting Ltd | Administrative & support | 2011 |
| James Holton HIP and Knee Services Ltd | Health & social care | 2026 |
| James Mason Trading Limited | Financial services | 2017 |
| James Pond Ltd | Wholesale & retail | 2009 |
| Jamie Briggs Removals and Storage Limited | Transport & logistics | 2002 |
| Jane Cheel Furniture Limited | Manufacturing | 2013 |
| Jane Deith Broadcasting Limited | Information & communication | 2013 |
| Janssens Consulting Limited | Professional & scientific | 1999 |
| Jason Vance Project Management Ltd | Administrative & support | 2010 |
| Jasutis Consulting Limited | Professional & scientific | 2023 |
| Jayanshayan Ltd | Real estate | 2023 |
| JB Risk Solutions Ltd | Information & communication | 2024 |
| JCC Electrical Ltd | Construction | 2012 |
| JCC Fire & Security Ltd | Construction | 2026 |
| JCC Solar Ltd | Construction | 2023 |
| JCJ PR and Marketing Limited | Professional & scientific | 2008 |
| JCS Plus Limited | Construction | 2014 |
| Jcshop Limited | Wholesale & retail | 2023 |
| JDM Finance Solutions Limited | Financial services | 2008 |
| Jdrm Dental Care Limited | Health & social care | 2009 |
| Jdvisuals Ltd | Information & communication | 2026 |
| Jelanika Limited | Professional & scientific | 2018 |
| Jenki Investments Limited | Financial services | 2017 |
| Jenkins & Blenheim Ltd | Administrative & support | 2026 |
| Jennie Younger Consultancy Ltd | Professional & scientific | 2015 |
| Jeremiah Media Ltd | Information & communication | 2025 |
| Jersey Arms (Biscester) Ltd | Hospitality | 2024 |
| Jersey Arms Bar Ltd | Wholesale & retail | 2025 |
| Jfci Limited | Information & communication | 2024 |
| Jfcpm Ltd | Construction | 2017 |
| JG Broadcast Jibs Limited | Information & communication | 2015 |
| JG Meded Consultancy Ltd | Health & social care | 2024 |
| JGS Enterprises Limited | Wholesale & retail | 2001 |
| Jiji Estates Limited | Real estate | 2021 |
| Jimma Jamma Lulu Limited | Information & communication | 2016 |
| Jinweiwang Ltd | Hospitality | 2026 |
| JJ Consulting Services (Oxon) Ltd | Extraterritorial | 2025 |
| JJ London Ltd | Wholesale & retail | 2019 |
| JK Green Pastures Ltd | Administrative & support | 2026 |
| JK Lifting Ltd | Construction | 2015 |
| JKG Investments Ltd | Real estate | 2021 |
| JKG Property Trading Ltd | Real estate | 2021 |
| JL Consulting Limited | Professional & scientific | 2020 |
| Jlca Limited | Wholesale & retail | 2023 |
| JLR London Leather Goods Limited | Wholesale & retail | 2009 |
| JM Electrical & Testing Ltd | Construction | 2026 |
| JM Gunn Groundwork Limited | Construction | 2005 |
| Jmdpropertyuk Ltd | Real estate | 2019 |
| JME (Housing Procurement) Consultancy Limited | Professional & scientific | 2016 |
| JME HR Solutions Ltd | Administrative & support | 2011 |
| Jmrc 60 Ltd | Professional & scientific | 2019 |
| Jmrc Pensions Limited | Professional & scientific | 2012 |
| JO Hedley Ltd | Professional & scientific | 2013 |
| Joao Souteiro Ltd | Health & social care | 2021 |
| Joblings Garage Limited | Real estate | 1996 |
| Johan RD Limited | Manufacturing | 2022 |
| John Bartleet Property Limited | Extraterritorial | 2023 |
| John Clavell Bate Limited | Health & social care | 2012 |
| John Ward Fencing Limited | Wholesale & retail | 2022 |
| Johnston & Lewis Limited | Professional & scientific | 2017 |
| Johnstown Convenient Store Limited | Wholesale & retail | 2021 |
| Johnstown PO Limited | Wholesale & retail | 2022 |
| Johnstown Premier Property Limited | Wholesale & retail | 2021 |
| Johnyck Brothers Limited | Transport & logistics | 2016 |