| James Place Property LLP | | 2025 |
| James Rose Accountancy Limited | Professional & scientific | 2024 |
| James Tasker Limited | Professional & scientific | 2024 |
| Jamie Edgell Limited | Professional & scientific | 2008 |
| Jamie Wagland PT Limited | Arts & recreation | 2019 |
| Jane Brown Associates Limited | Professional & scientific | 2007 |
| Jane WEI London Limited | Professional & scientific | 2016 |
| Janty Property Limited | Real estate | 2011 |
| Japanese Head Spa Therapy Ltd | Other services | 2024 |
| JAR Drinks Group Ltd | Manufacturing | 2023 |
| Jarp & Co LLP | | 2025 |
| JAS Apparel Ltd | Wholesale & retail | 2021 |
| Jasada Ltd | Financial services | 2026 |
| Jascar Logistics Limited | Transport & logistics | 2008 |
| Jasmine Holidays Limited | Administrative & support | 2007 |
| Javlin Ltd | Information & communication | 2012 |
| Jawher Ltd | Hospitality | 2026 |
| JAX Retail Ltd | Wholesale & retail | 2024 |
| Jaxa Consultancy Limited | Information & communication | 2023 |
| JAY Berg Design Limited | Information & communication | 1997 |
| Jayseemotors Limited | Administrative & support | 2025 |
| Jazandon Limited | Extraterritorial | 2016 |
| JB Capital Consulting Ltd | Wholesale & retail | 2025 |
| Jb-Nomo Ltd | Professional & scientific | 2026 |
| JC Sales Consulting Ltd | Professional & scientific | 2023 |
| Jc&A Consulting Limited | Professional & scientific | 2017 |
| Jcaj Property Holding Limited | Real estate | 2025 |
| JCF Somerset Ltd | Real estate | 2023 |
| JCG Wood Ltd | Real estate | 2024 |
| JCS Service Solutions LLP | | 2019 |
| Jctjl Limited | Real estate | 2015 |
| JCW Brands & Consulting Ltd | Wholesale & retail | 2018 |
| JD Developments (London) Limited | Real estate | 2006 |
| JD Food Ltd | Hospitality | 2025 |
| JDC Sun Properties Limited | Hospitality | 2022 |
| JDC Tooth DOC Ltd | Health & social care | 2008 |
| JDM Health and Fitness Limited | Health & social care | 2015 |
| JDO 2 Ltd | Professional & scientific | 2012 |
| JDO Group Limited | Professional & scientific | 2014 |
| JDO Group Trustees Limited | Professional & scientific | 2026 |
| JDO Ltd | Professional & scientific | 2003 |
| JDR Business Consulting Ltd | Professional & scientific | 2024 |
| JDR Network Services Limited | Information & communication | 2012 |
| JE Equine Limited | Education | 2020 |
| Jell Limited | Administrative & support | 2006 |
| Jellu Ltd | Information & communication | 2024 |
| Jerama Publications LLP | | 2021 |
| Jessbuildstech Ltd | Information & communication | 2026 |
| Jetsun Creative Ltd | Professional & scientific | 2017 |
| Jettabox Group Ltd | Wholesale & retail | 2023 |
| Jfeh Holdings Ltd | Financial services | 2025 |
| JG Legal Consulting Limited | Professional & scientific | 2014 |
| JGL Brickwork Ltd | Construction | 2024 |
| Jgss Ltd | Professional & scientific | 2017 |
| Jhae Holdings Ltd | Financial services | 2025 |
| Jhood Labs Ltd | Information & communication | 2025 |
| Jigsaw Fine Art Remote Adjusting Services Ltd | Financial services | 2026 |
| Jigsaw Five Limited | Financial services | 2023 |
| Jigsaw Four Ltd | Financial services | 2021 |
| Jigsaw One Ltd | Financial services | 2018 |
| Jigsaw Seven Limited | Financial services | 2025 |
| Jigsaw SIX Limited | Financial services | 2023 |
| Jigsaw Three Ltd | Financial services | 2022 |
| Jigsaw Two Ltd | Financial services | 2020 |
| JIM Litchfield Motor Engineer Limited | Wholesale & retail | 2009 |
| Jimhunty Ltd | Information & communication | 2015 |
| Jiskoot Solutions Ltd | Professional & scientific | 2019 |
| JJJ Vano Limited | Professional & scientific | 2016 |
| JKL Traders Limited | Wholesale & retail | 2012 |
| JKM Brothers Limited | Real estate | 2024 |
| JKS Communications International Ltd | Administrative & support | 2005 |
| JL Utilities UK Limited | Professional & scientific | 2006 |
| JLB IT Solutions Limited | Administrative & support | 2014 |
| Jljm Ltd | Administrative & support | 2023 |
| JLM Pest Control Ltd | Administrative & support | 2018 |
| JLR Utility Services Limited | Construction | 2010 |
| Jlrsearch Ltd | Administrative & support | 2024 |
| JM Bathroom Renovations Ltd | Construction | 2023 |
| JM Wright Consulting Ltd | Professional & scientific | 2025 |
| Jmcr Limited | Information & communication | 2024 |
| JMH Development Services Limited | Information & communication | 2005 |
| JMK Services Ltd | Administrative & support | 2024 |
| Jmrb Consulting Ltd | Professional & scientific | 2022 |
| Jnctsk Holdings Limited | Financial services | 2023 |
| Jnhcreative Ltd | Professional & scientific | 2023 |
| JNL Total Building Solutions Ltd | Construction | 2023 |
| John Atherton Limited | Professional & scientific | 2008 |
| John Hayes-Fisher Productions Limited | Information & communication | 2009 |
| John Sampson,Limited | Real estate | 1933 |
| John Thomas Advice Ltd | Professional & scientific | 2025 |
| John Wall Developments Ltd | Real estate | 2014 |
| Johnson and Allen Property Limited | Professional & scientific | 2004 |
| Johnson Land Services Ltd | Other services | 2026 |
| Join Together Co-Operative Limited | Information & communication | 2021 |
| Jolly Grocer Ltd | Wholesale & retail | 2022 |
| Joloca Limited | Professional & scientific | 2020 |
| Jolt Studio Limited | Information & communication | 2017 |
| JON Tibbs Associates (Holdings) Limited | Professional & scientific | 2013 |
| JON Tibbs Associates Limited | Professional & scientific | 2008 |
| Jon's Bespoke Home Catering Ltd | Hospitality | 2025 |