| Ivor Henry Ltd | Professional & scientific | 2025 |
| Izon Science Europe Ltd | Professional & scientific | 2009 |
| J a Feed Services Limited | Agriculture & fishing | 2020 |
| J Churcher Consulting Ltd | Professional & scientific | 2024 |
| J Dell Carpentry Ltd | Manufacturing | 2025 |
| J P Snooks Limited | Construction | 2006 |
| J R Plumbing & Heating Oxon Limited | Construction | 2015 |
| J. Rixon Limited | Agriculture & fishing | 1991 |
| J.D Thame Ltd | Hospitality | 2026 |
| Jacaranda Archives Limited | Administrative & support | 2000 |
| Jade Tree Coaching Ltd | Professional & scientific | 2025 |
| James Smith (Planning Law Services) Limited | Professional & scientific | 2011 |
| Jamie Cassettari Construction Limited | Construction | 2025 |
| Janus Conservation Ltd | Construction | 2019 |
| Japhex Limited | Information & communication | 2015 |
| Jarvis Engineering Limited | Professional & scientific | 1945 |
| Jasmel Limited | Wholesale & retail | 2018 |
| Jasteq Limited | Information & communication | 2014 |
| Jayamohan Limited | Professional & scientific | 2011 |
| JCI Bradley Limited | Professional & scientific | 2019 |
| Jenveytech Consulting Ltd | Information & communication | 2025 |
| Jerali Healthcare Ltd | Health & social care | 2026 |
| Jerina Communications Ltd | Professional & scientific | 2019 |
| Jessica ZOE Divorce Coach Ltd | Extraterritorial | 2025 |
| JET Black Raider Ltd | Information & communication | 2018 |
| JFB Medical Limited | Health & social care | 2016 |
| Jigsaw Futures Ltd | Health & social care | 2015 |
| JIM Thompson Consulting Limited | Professional & scientific | 2008 |
| JJS Minerals INT. Limited | Mining & quarrying | 2014 |
| JJS Resources Co Ltd | Mining & quarrying | 2023 |
| Jkha Ltd | Professional & scientific | 2026 |
| JM MSK Ltd | Health & social care | 2025 |
| JMH Lusby Ltd. | Information & communication | 1998 |
| Jmhj Properties Limited | Real estate | 2022 |
| JNJ Limited | Manufacturing | 2000 |
| Jocie Juritz Collection Ltd | Wholesale & retail | 2022 |
| John Alexander Lowe Colour Ltd | Arts & recreation | 2024 |
| John Boyd Motor Repairs Limited | Wholesale & retail | 2002 |
| Jonathan Marilleau Consulting Limited | Professional & scientific | 2017 |
| Jonathan Marilleau Ltd | Wholesale & retail | 2018 |
| Jordan Family Holdings Limited | Real estate | 2024 |
| Jordan Nelson Design Ltd | Professional & scientific | 2019 |
| Jordell Limited | Wholesale & retail | 2007 |
| JP Equestrian LLP | | 2015 |
| JR2020 Limited | Professional & scientific | 2022 |
| JRS Electrical Services Limited | Construction | 2015 |
| Julia Nagle Conservation Limited | Professional & scientific | 2009 |
| Julian Carthew Sales and Lettings Limited | Real estate | 2005 |
| Jyst Creative Limited | Information & communication | 2010 |
| K L Brick & Building Services Limited | Construction | 2008 |
| K-Tee Artist Ltd | Information & communication | 2016 |
| Kagem Properties Limited | Households | 2004 |
| KAL Clifford Ltd | Real estate | 2019 |
| Kali Cafe Ltd | Hospitality | 2024 |
| Kalsi Design Limited | Professional & scientific | 2021 |
| Kama Cars Ltd | Wholesale & retail | 2012 |
| Kamwell Limited | Health & social care | 2013 |
| Karem Consulting Limited | Professional & scientific | 2013 |
| Kasar Limited | Professional & scientific | 2009 |
| Kate Oliver Coaching Limited | Administrative & support | 2022 |
| Kath Norkett Financial Planning Ltd | Financial services | 2020 |
| Katherine Cowan Consulting Limited | Professional & scientific | 2012 |
| KC4BUSINESS Limited | Administrative & support | 2015 |
| Kdsc Limited | Information & communication | 2003 |
| Kelley Waters Ltd | Health & social care | 2003 |
| Kenmilquin Booster BOY Ltd | Information & communication | 2019 |
| Kennett Financial Management Ltd | Professional & scientific | 2010 |
| Keogh Photography Limited | Professional & scientific | 2017 |
| Kepler Energy Limited | Professional & scientific | 2025 |
| Kesw Ltd | Construction | 2025 |
| KEW Green Limited | Administrative & support | 2019 |
| KEW Sales Ltd | Professional & scientific | 2014 |
| Key Channel Limited | Wholesale & retail | 2015 |
| Keypoynt Ltd | Professional & scientific | 2024 |
| Kidskonnect UK Holding Limited | Financial services | 2023 |
| Kieren Spencer Limited | Health & social care | 2007 |
| King Brown Limited | Administrative & support | 2013 |
| King Hunt Limited | Financial services | 2023 |
| Kingdom Projects (UK) Limited | Professional & scientific | 2013 |
| Kjmd Human Resources Consultancy Ltd | Administrative & support | 2014 |
| Klafs UK Limited | Construction | 2000 |
| Kopru PR Limited | Professional & scientific | 2025 |
| Koriander Holdings Ltd | Administrative & support | 2017 |
| Kremmen Group Limited | Financial services | 2022 |
| Kremmen Servicing Limited | Real estate | 1987 |
| Kudu Estates Ltd | Real estate | 2020 |
| Kunkune Limited | Wholesale & retail | 2020 |
| LA Casa Solutions Ltd | Professional & scientific | 2020 |
| LA Mariposa Polo Limited | Arts & recreation | 2008 |
| La-Eva Limited | Manufacturing | 2016 |
| Laboris Solutions Limited | Administrative & support | 2020 |
| Ladderhill Projects Ltd | Information & communication | 2025 |
| Lambs Fitness Ltd | Arts & recreation | 2026 |
| Landmark Garden Design & Construction Ltd | Administrative & support | 2019 |
| Lankport Limited | Other services | 1979 |
| Latchford Developments Limited | Construction | 2022 |
| Launch Lens Ltd | Professional & scientific | 2015 |
| Lawgorithm Limited | Professional & scientific | 2017 |
| Lcmr Associates Limited | Professional & scientific | 2020 |
| Leap Architects Ltd | Professional & scientific | 2018 |