| J K Lake Properties Ltd | Real estate | 2023 |
| J L Design & Build Limited | Construction | 2013 |
| J R Green Newsagents Limited | Wholesale & retail | 2019 |
| J R Rolfe Limited | Construction | 2003 |
| J White Plumbing & Heating Ltd | Construction | 2014 |
| J&D Estates and Investments Limited | Real estate | 2022 |
| J&L Financial Ltd | Real estate | 2025 |
| J&S Products Limited | Administrative & support | 2016 |
| J&S Sinus Ltd | Transport & logistics | 2020 |
| J-Camison Limited | Wholesale & retail | 2026 |
| J-M-F Building Services Ltd | Construction | 2020 |
| J. & A.G. Burton Limited | Wholesale & retail | 1976 |
| J. Bedford Construction Limited | Construction | 2015 |
| J. Singh Transport Ltd | Transport & logistics | 2003 |
| J. Woodcock Ltd | Construction | 2005 |
| J.A. Searle & Sons Limited | Agriculture & fishing | 1998 |
| J.H. Jones Ltd | Professional & scientific | 2025 |
| J.R. Eyewear Ltd | Wholesale & retail | 2023 |
| J.R.C. Waveney Limited | Real estate | 2006 |
| J.Sins Logistics Ltd | Transport & logistics | 2018 |
| JA Willbless Ltd | Health & social care | 2023 |
| Jaanda Holdings Limited | Financial services | 2018 |
| Jabie Ltd | Hospitality | 2024 |
| Jack Retail Ltd | Wholesale & retail | 2012 |
| Jackson Ward Developments Ltd | Construction | 2006 |
| Jacowe Joinery Limited | Construction | 1979 |
| Jades on the Weald Ltd | Other services | 2025 |
| Jagged Edge Academy Ltd | Education | 2019 |
| JAH (Cambridge) Limited | Administrative & support | 2012 |
| Jaipur Furniture Limited | Wholesale & retail | 2007 |
| Jakabar Limited | Extraterritorial | 2010 |
| James COX Limited | Wholesale & retail | 2007 |
| James Gillan Limited | Information & communication | 2026 |
| James Gingell Consultancy Limited | Information & communication | 2026 |
| James Hurley - Art Ltd | Wholesale & retail | 2023 |
| James Property Partners Ltd | Real estate | 2023 |
| James Winton Limited | Financial services | 2012 |
| James, Jack and Jacobs Ltd | Real estate | 2022 |
| JAN Tyres Automotive Ltd | Wholesale & retail | 2019 |
| Jandee Property Company Limited | Real estate | 2021 |
| Janus Drug Discovery Consulting Ltd | Professional & scientific | 2023 |
| Jarlights Associates Limited | Administrative & support | 2017 |
| Jarwood Property Ltd | Real estate | 2026 |
| Jasmar Timber Products Limited | Wholesale & retail | 2013 |
| Jasmin Consultancy Services Limited | Health & social care | 2016 |
| Jason Pope Ltd | Construction | 2020 |
| Jason White Plumbing & Heating Limited | Construction | 2024 |
| Jasta Binks Aviation Limited | Manufacturing | 2006 |
| Jatz Properties Ltd | Real estate | 2022 |
| JAY Dalgarno Media Ltd | Information & communication | 2026 |
| Jayling Renovations Limited | Construction | 2017 |
| Jayrich Limited | Information & communication | 2006 |
| JB Bespoke Drylining Ltd | Extraterritorial | 2024 |
| JB Insight Services Ltd | Professional & scientific | 2022 |
| Jb&Lvk Limited | Professional & scientific | 2021 |
| JBC Homes Ltd | Construction | 2024 |
| JBR Homes Ltd | Real estate | 2019 |
| JBR Structures Ltd | Construction | 2025 |
| Jbsr Ltd | Financial services | 2018 |
| JC Healthcare Limited | Health & social care | 2025 |
| JC Training Ltd | Professional & scientific | 2022 |
| JCC Performance Ltd | Manufacturing | 2025 |
| JCD Security Solutions Limited | Construction | 2015 |
| JCT Digital Ltd | Information & communication | 2025 |
| JDH Growth Ltd | Professional & scientific | 2026 |
| Jencol Engineering Limited | Manufacturing | 2003 |
| Jennifer Moodie Associates Limited | Professional & scientific | 2010 |
| Jenny Garcia Ltd | Health & social care | 2020 |
| Jensten Group Limited | Financial services | 2012 |
| Jensten Holdings Limited | Financial services | 2018 |
| Jensten Insurance Brokers Limited | Financial services | 2012 |
| Jensten Risk Management Limited | Wholesale & retail | 2026 |
| Jensten Technologies Limited | Information & communication | 1985 |
| Jensten Underwriting (Bespoke) Limited | Financial services | 2006 |
| Jensten Underwriting (Commercial) Limited | Financial services | 2005 |
| Jensten Underwriting (SME) Limited | Financial services | 2012 |
| Jeremy Moorman Payments Consulting Limited | Professional & scientific | 2015 |
| Jerry’S Burgers and More Ltd | Hospitality | 2024 |
| Jetbadger Limited | Information & communication | 2011 |
| Jezdav Trading Limited | Hospitality | 2026 |
| Jezi Mama Ltd | Wholesale & retail | 2021 |
| JF Wealth Management Ltd | Professional & scientific | 2014 |
| Jfftechnolgy Ltd | Manufacturing | 2026 |
| Jfftechnology Ltd | Manufacturing | 2026 |
| JG Pipe Solutions Ltd | Construction | 2018 |
| JGL Bidco 1 Limited | Financial services | 2020 |
| JGL Bidco 2 Limited | Financial services | 2020 |
| JGL Bidco 3 Limited | Financial services | 2021 |
| JGL Bidco 4 Limited | Financial services | 2023 |
| JGL Bidco 5 Limited | Financial services | 2023 |
| JGL Bidco 6 Limited | Financial services | 2023 |
| JGL Bidco 7 Limited | Financial services | 2023 |
| JGL Bidco 8 Limited | Financial services | 2023 |
| JGL Bidco 9 Limited | Financial services | 2025 |
| JH Bookkeeping Services Ltd | Other services | 2019 |
| JH International Ltd | Extraterritorial | 2025 |
| JH Truckstyling Limited | Wholesale & retail | 2022 |
| Jhun Hart Limited | Health & social care | 2021 |
| Jibby AI Ltd | Information & communication | 2025 |
| JJ Parts UK Ltd | Other services | 2015 |