| J&B Travel Group Ltd | Information & communication | 2024 |
| J&Cocameras Limited | Information & communication | 2025 |
| J&K Property (Herts) Ltd | Construction | 2026 |
| J&R Construction Group Ltd | Construction | 2017 |
| J. Stock Trading Ltd | Real estate | 2024 |
| J.A.B.S. Productions Ltd | Information & communication | 2024 |
| J.B. Armstrong Construction Ltd | Construction | 2019 |
| J.E.K. Associates Limited | Professional & scientific | 2009 |
| J.H.P Foods Limited | Real estate | 1994 |
| J.J. Burgess & Sons Limited | Extraterritorial | 2002 |
| J12 Ventures Nordic I Tr-A SPV LLP | | 2022 |
| J12 Ventures Nordic I Ze-S SPV LLP | | 2023 |
| J2J Investments Limited | Real estate | 2025 |
| J50 Limited | Real estate | 2014 |
| JAB Boxing Club Ltd | Arts & recreation | 2022 |
| JAB Boxing Holdings Ltd | Arts & recreation | 2025 |
| JAB Operations Limited | Financial services | 2025 |
| Jabriya Capital LLP | | 2020 |
| Jabs Medtech Ltd. | Information & communication | 2023 |
| JAC Welding Services Ltd. | Professional & scientific | 2013 |
| Jackson Kent Associates Ltd | Information & communication | 1997 |
| Jacob Frum Limited | Administrative & support | 2012 |
| Jadison Ltd | Professional & scientific | 2024 |
| Jaga Steel Frames and Cladding Ltd | Construction | 2025 |
| Jake Charles Property Ltd | Real estate | 2021 |
| Jake's Bake Limited | Wholesale & retail | 2025 |
| JAM Bookkeeping Services Ltd | Professional & scientific | 2019 |
| JAM Foods Ltd | Wholesale & retail | 2019 |
| JAM Gardens Ltd | Administrative & support | 2022 |
| James Court Residents Company Limited | Real estate | 2000 |
| James Joseph Ltd | Financial services | 2022 |
| James Owen Consulting Limited | Professional & scientific | 2015 |
| James Russell Consulting Ltd | Professional & scientific | 2020 |
| James Tiley Health & Fitness Ltd | Education | 2021 |
| Jamie Orlando Smith Limited | Professional & scientific | 2015 |
| Jamiebreeno Ltd | Education | 2025 |
| Jamietennis Ltd | Arts & recreation | 2013 |
| Jamm Limited | Manufacturing | 2022 |
| JAN B Consultancy Limited | Professional & scientific | 2015 |
| JAN Consultancy Ltd | Professional & scientific | 2019 |
| Jane's Swim School Limited | Arts & recreation | 2011 |
| Janes Care Homes Limited | Health & social care | 2003 |
| Janes Property Investments Limited | Real estate | 2024 |
| Janev Lettings Ltd | Real estate | 2026 |
| Janine Robin UK Ltd | Wholesale & retail | 2024 |
| Jardine-White Consulting Limited | Administrative & support | 2015 |
| Jarrad Consulting Limited | Information & communication | 2017 |
| Jarvis Bay Limited | Real estate | 2015 |
| Jash Homes Ltd | Real estate | 2021 |
| Jasi Investments LLP | | 2014 |
| Jasminous Ltd | Extraterritorial | 2020 |
| Jason Davies Limited | Information & communication | 2005 |
| Jason George Consulting Ltd | Professional & scientific | 2026 |
| Jaspers Hire Limited | Other services | 1997 |
| Javeria Ltd | Wholesale & retail | 2026 |
| Jayne Reah Ltd | Administrative & support | 2020 |
| Jazz-Works Limited | Professional & scientific | 2012 |
| JB Carconcept (UK) Ltd | Administrative & support | 2019 |
| JB Property and Construction Services Ltd | Construction | 2022 |
| Jb&Bc Ltd | Information & communication | 2025 |
| Jbjb Limited | Construction | 2025 |
| JBP Developments Ltd | Construction | 2015 |
| JBS Community Workshops CIC | Professional & scientific | 2025 |
| JC Electrical Testing Ltd | Construction | 2025 |
| JC Independent Wills & Probate Ltd | Professional & scientific | 2010 |
| JC Lenus Primary SPV LLP | | 2023 |
| JC Lenus Secondary SPV LLP | | 2023 |
| JC UK Supplies Ltd | Wholesale & retail | 2025 |
| JCL Renovations Ltd | Construction | 2018 |
| Jcmb Estates Ltd | Real estate | 2024 |
| Jctc Properties Limited | Real estate | 2003 |
| JD Healthcare & Management Consultancy Ltd | Health & social care | 2016 |
| Jdaa Electrical Services Ltd | Construction | 2026 |
| JDB Law Ltd | Professional & scientific | 2022 |
| Jearni Ltd | Information & communication | 2024 |
| Jebba Consulting and Trading Limited | Professional & scientific | 2014 |
| Jefferson Eco CIC | Wholesale & retail | 2023 |
| Jeffersons Estate Agents Limited | Households | 1994 |
| Jegede Build Ltd | Construction | 2026 |
| Jekab Agency Ltd | Administrative & support | 2026 |
| JEL Financial Services Ltd | Financial services | 2026 |
| Jelly Bros Ltd | Wholesale & retail | 2026 |
| JEM Consulting Enterprise Limited | Information & communication | 2025 |
| Jenkins Property Holdings Ltd | Real estate | 2019 |
| Jennings Financial Consultants Limited | Professional & scientific | 2015 |
| Jeremy Hazlehurst Editorial Ltd | Information & communication | 2013 |
| Jess Jarrold Coaching Ltd | Professional & scientific | 2024 |
| Jessamine Motor Company Ltd | Wholesale & retail | 1995 |
| Jessella Roofing Limited | Construction | 2020 |
| JET Black Squares Ltd | Professional & scientific | 2020 |
| Jewel Fruits Limited | Wholesale & retail | 2020 |
| Jewell of Watford (1986) Limited | Transport & logistics | 1974 |
| Jeznico Studios Ltd | Professional & scientific | 2020 |
| JF Carpentry Services Ltd | Manufacturing | 2026 |
| JF Lighting Ltd | Arts & recreation | 2021 |
| JFK Gardening Limited | Administrative & support | 2026 |
| JGP Services Ltd | Manufacturing | 2025 |
| JGS Coaching Ltd | Education | 2026 |
| JH Touring Ltd | Administrative & support | 2026 |
| Jialca Ltd | Information & communication | 2015 |