| Iturri, Limited | Wholesale & retail | 1996 |
| Ivison Transport Limited | Transport & logistics | 2014 |
| Ivywilduk Limited | Wholesale & retail | 2022 |
| Izod Farming Limited | Agriculture & fishing | 2003 |
| J & B Heritage Ltd | Construction | 2019 |
| J & B Lefevre (Redlion Culworth) Limited | Hospitality | 2009 |
| J & BS Ltd | Extraterritorial | 2007 |
| J & J Associates (UK) Ltd. | Professional & scientific | 2013 |
| J & J Brinklow Holdings Limited | Professional & scientific | 2020 |
| J & J Decorating Ltd | Construction | 2015 |
| J a G W Medical Services LLP | | 2012 |
| J C Bernardes Ltd | Transport & logistics | 2020 |
| J D'Cruz Limited | Wholesale & retail | 2012 |
| J F Boasman Ltd | Professional & scientific | 2013 |
| J G Home and Roof Ltd | Construction | 2026 |
| J Harrison Construction Solutions Ltd | Construction | 2015 |
| J J Brooks Limited | Agriculture & fishing | 2004 |
| J J Cummings Limited | Construction | 2015 |
| J J Performance Engineering Limited | Wholesale & retail | 2012 |
| J L D Driver Training Limited | Administrative & support | 2008 |
| J L W Accountancy Services Limited | Professional & scientific | 2023 |
| J Mills Property Ltd | Real estate | 2020 |
| J P Lifting Limited | Construction | 2003 |
| J W Bespoke Homes Ltd | Construction | 2020 |
| J W Lewis Electrical Ltd | Construction | 2018 |
| J W Trims Ltd | Other services | 2025 |
| J Wentzel Enterprises Ltd | Information & communication | 2017 |
| J&B Health Solutions Ltd | Professional & scientific | 2015 |
| J. T. W. Flooring Ltd | Construction | 2012 |
| J.A. Buildings Limited | Real estate | 2002 |
| J.D. COX Farms Limited | Agriculture & fishing | 1981 |
| J.M.F Transport Solutions Ltd | Transport & logistics | 2025 |
| J.Smith & Sons(Walters Ash),Limited | Construction | 1934 |
| J.T. Heating Limited | Construction | 2001 |
| Jaagal Foods Ltd | Wholesale & retail | 2025 |
| JAC Corporate Services Limited | Professional & scientific | 1996 |
| Jack D. Services Ltd | Transport & logistics | 2016 |
| Jack Whip Inns Ltd | Hospitality | 2025 |
| Jackola Ltd | Manufacturing | 2013 |
| Jackson Sammons Limited | Real estate | 2025 |
| Jacobs Douwe Egberts OPS GB Ltd | Manufacturing | 2015 |
| Jadoon Apparel Ltd | Wholesale & retail | 2025 |
| Jaid Solutions Ltd | Information & communication | 2016 |
| Jake Tyrrell Safety Limited | Professional & scientific | 2018 |
| Jake Whittingham Limited | Arts & recreation | 2017 |
| Jakeman Reclaim & Roofing Ltd | Wholesale & retail | 2016 |
| Jakes Overland Adventures Ltd | Wholesale & retail | 2024 |
| Jakku Ventures Ltd | Professional & scientific | 2023 |
| James & Mathew Ltd | Wholesale & retail | 2020 |
| James Boswell Hair Design Ltd | Other services | 2026 |
| James Bros. (Building Services Contractor) Ltd | Wholesale & retail | 1995 |
| James Buck Films Limited | Information & communication | 2018 |
| James Hudson Consulting Ltd | Professional & scientific | 2022 |
| Jamie Phillips Photography Ltd | Professional & scientific | 2023 |
| Jampackedclearances Ltd | Wholesale & retail | 2025 |
| Jara Transport Ltd | Construction | 2016 |
| Jarla Investment Limited | Extraterritorial | 2012 |
| Jasah Ltd | Administrative & support | 2020 |
| Jason Onions Building Solutions Limited | Construction | 2014 |
| Jason Tubb Limited | Construction | 2013 |
| Javine Ltd | Professional & scientific | 2026 |
| JAW Engineering Services Limited | Manufacturing | 2025 |
| JAY Bonney Medical and Transportation Ltd | Health & social care | 2018 |
| Jaydee Motors Limited | Wholesale & retail | 2001 |
| Jayetarms Limited | Other services | 2025 |
| Jayp Autos Ltd | Wholesale & retail | 2022 |
| JCG Walk, Play and Stay Ltd | Other services | 2025 |
| JCH Capital Ltd | Wholesale & retail | 2021 |
| JDA Multi-Services Ltd | Professional & scientific | 2025 |
| JDS Capital Limited | Financial services | 2023 |
| JDS Strategists Ltd | Professional & scientific | 2020 |
| Jenks Oxford Limited | Agriculture & fishing | 2003 |
| Jenn's Cleaning Ltd | Administrative & support | 2021 |
| Jennifer Turner Limited | Other services | 2003 |
| Jenno Ltd | Financial services | 2022 |
| Jennys Cafe Ltd | Hospitality | 2019 |
| Jensen International Automotive Limited | Manufacturing | 2010 |
| Jensen International Group Limited | Financial services | 2025 |
| Jensen UK Limited | Manufacturing | 1998 |
| Jensen Works Limited | Manufacturing | 2015 |
| Jerry's Rope Access and Civil Engineering Services Limited | Construction | 2012 |
| Jerwood Foundation | Other services | 2021 |
| Jerwood Limited | Extraterritorial | 2025 |
| Jerzy Trans Ltd | Transport & logistics | 2016 |
| Jess and JO Limited | Hospitality | 2026 |
| Jess Hall Physiotherapy Ltd | Professional & scientific | 2025 |
| Jeyaram Limited | Wholesale & retail | 2023 |
| JGM Renewables Ltd | Construction | 2024 |
| JH Hairdressing Ltd | Other services | 2017 |
| JH Ravrani Academy Limited | Education | 2021 |
| JH80 Consulting Limited | Administrative & support | 2025 |
| Jhdp Capital Ltd | Wholesale & retail | 2025 |
| JHG Productions Limited | Administrative & support | 2024 |
| Jhri Capital Ltd | Information & communication | 2026 |
| JHS Development Services Ltd | Manufacturing | 2024 |
| Jilly Hunt Publishing Services Ltd | Administrative & support | 2021 |
| JJ Consulting (Oxon) Limited | Professional & scientific | 2010 |
| JJ Express Deliveries Ltd | Transport & logistics | 2026 |
| JJA Enterprises Ltd | Agriculture & fishing | 2021 |
| JJZ Noor Limited | Administrative & support | 2024 |