| J-Greats Ltd | Extraterritorial | 2022 |
| J-Greats Properties Ltd | Real estate | 2022 |
| J. a. Pell & SON Limited | Construction | 2023 |
| J. Brown Flooring Limited | Construction | 2007 |
| J. Carson Signalling Services Limited | Administrative & support | 2007 |
| J. M. Briggs Property Services Limited | Real estate | 2015 |
| J.A Gardens Limited | Construction | 2017 |
| J.A.L. Investments Limited | Administrative & support | 1998 |
| J.H.Desmond Limited | Financial services | 1946 |
| J.Myers Ltd | Transport & logistics | 2026 |
| J2 Property Ltd | Real estate | 2021 |
| Jack Conner Designs Ltd | Wholesale & retail | 2005 |
| Jack Green Limited | Administrative & support | 2017 |
| Jack Winer Golf Ltd | Wholesale & retail | 2020 |
| Jackson Media Limited | Professional & scientific | 2016 |
| Jaerndal Ltd | Real estate | 2012 |
| Jaffaria Academy Ltd | Education | 2020 |
| Jafrabad Ltd | Hospitality | 2018 |
| JAG OPS Limited | Hospitality | 2025 |
| Jagajendi LLP | | 2011 |
| Jaguar Shoes Limited | Extraterritorial | 2014 |
| JAH (London) Properties Limited | Real estate | 2024 |
| Jaha@Sons Ltd | Construction | 2021 |
| Jaic Consultancy Ltd | Construction | 2016 |
| Jaic Properties Limited | Real estate | 2022 |
| Jakaria Ventures Ltd | Wholesale & retail | 2025 |
| Jake Jackman Properties Ltd | Real estate | 2019 |
| Jakes Food & Wine Limited | Administrative & support | 2004 |
| JAM Video Services Limited | Information & communication | 2019 |
| James Bridge Productions Limited | Information & communication | 2011 |
| James Hallybone Limited | Construction | 1985 |
| James Leal Cafe Ltd | Hospitality | 2020 |
| James Quinn AI Designs Ltd | Information & communication | 2021 |
| James R. Williams Ltd | Information & communication | 2018 |
| James Rhodes Ltd | Administrative & support | 2010 |
| James-Anjum Associates Limited | Professional & scientific | 2006 |
| Jammy Tots Nursery Ltd | Health & social care | 2025 |
| Jannie Sweetman Ltd | Construction | 2014 |
| Jant Group Holdings Limited | Financial services | 2021 |
| Jant Property Holdings Limited | Financial services | 2021 |
| Jarrison Construction and Consultancy Limited | Construction | 2004 |
| JAS Buildings Limited | Construction | 2017 |
| Jase Limited | Administrative & support | 1999 |
| Jasmine and Chic Ltd | Wholesale & retail | 2024 |
| Java Industries Limited | Real estate | 2022 |
| Jawsco Ltd | Administrative & support | 2022 |
| Jay-Bee (Portsmouth) Limited | Real estate | 1959 |
| JB Private Investments Ltd | Real estate | 2024 |
| JB UK Properties Ltd | Real estate | 2020 |
| Jbvj Properties Ltd | Real estate | 2024 |
| JC Diamonds Ltd | Wholesale & retail | 2016 |
| JCC Ventures Limited | Real estate | 2022 |
| Jcdirect Ltd | Wholesale & retail | 2025 |
| JCJ Consult Ltd | Professional & scientific | 2018 |
| JCJ Consult Services Ltd | Professional & scientific | 2026 |
| Jcls Consultancy Limited | Administrative & support | 2014 |
| Jc’S Aesthetics Ltd | Other services | 2023 |
| JD Major Decorating Services Ltd | Other services | 2013 |
| JD Tudor Construction Ltd | Construction | 2017 |
| JDB Productions Limited | Information & communication | 2017 |
| Jeff Professional Cleaners Ltd | Other services | 2014 |
| Jeffery Grant Developments Ltd | Construction | 2022 |
| Jellie Holdings Ltd | Administrative & support | 2025 |
| JEM Solutions (UK) Limited | Wholesale & retail | 2012 |
| Jenflo Properties Ltd | Real estate | 2025 |
| Jenkins Decorating Ltd | Construction | 2023 |
| Jenkins Decorators Ltd | Construction | 2014 |
| Jennings Enterprises Ltd | Extraterritorial | 2011 |
| Jennys (Wellingborough) Ltd | Hospitality | 2018 |
| Jenorm Limited | Real estate | 2011 |
| Jepson Theatre Productions Ltd | Arts & recreation | 2018 |
| Jesus Lives Bible Seminary - UK Limited | Other services | 2021 |
| JET CW Ltd | Other services | 2019 |
| JET Enterprises London Ltd | Construction | 2013 |
| Jetland LLP | | 2006 |
| Jets Property's Ltd | Real estate | 2024 |
| JEY Elite Care Services Limited | Health & social care | 2018 |
| JFA Capital Limited | Real estate | 2025 |
| JFC Marketing Limited | Administrative & support | 2026 |
| JFF Security Ltd | Administrative & support | 2019 |
| JFH Partnership Ltd | Other services | 2018 |
| JFM Cars Limited | Wholesale & retail | 2020 |
| JHC Group Ltd | Health & social care | 2023 |
| Jhpm Prop Ltd | Real estate | 2019 |
| Jigsaw + | Administrative & support | 2012 |
| Jigsaw Trading (2013) Limited | Education | 2013 |
| Jigsaw Training Limited | Administrative & support | 2023 |
| Jikky Limited | Information & communication | 2006 |
| JJ Group Ltd | Administrative & support | 2019 |
| Jj's Drinks Ltd | Manufacturing | 2025 |
| JK Aquila Ventures Limited | Real estate | 2019 |
| JK Wholesale Ltd | Wholesale & retail | 2025 |
| JKA Solutions Ltd | Information & communication | 2015 |
| JKL Media Limited | Information & communication | 2016 |
| JLB Connective Limited | Professional & scientific | 2011 |
| JLM Pharma Limited | Professional & scientific | 2024 |
| Jlmp Holdings Limited | Administrative & support | 2021 |
| Jlre Holdings Ltd | Real estate | 2026 |
| JMF Billing Services Ltd | Administrative & support | 2020 |
| JML Innovation Ltd | Real estate | 2021 |