| J.E.Q Construction Ltd | Construction | 2026 |
| J.F.D.I. Solutions Limited | Information & communication | 1997 |
| J.F.Long Ltd | Administrative & support | 2022 |
| J.Mikel Ltd | Administrative & support | 2010 |
| JA Construction UK Ltd | Construction | 2019 |
| JA Drylining Ltd | Construction | 2017 |
| JA Metrics Limited | Administrative & support | 2013 |
| JA Partners Ltd | Construction | 2017 |
| Jaan's Bakery and Deli Ltd | Manufacturing | 2026 |
| Jaask Invest Ltd | Real estate | 2025 |
| JAC Building Services Ltd | Construction | 2018 |
| JAC Property Maintainance Limited | Construction | 2019 |
| Jack Edwards Farms Limited | Agriculture & fishing | 2002 |
| Jack Mousley Limited | Education | 2021 |
| Jacob Grey Ltd | Administrative & support | 2020 |
| Jacobs & Neale Properties Ltd | Real estate | 2020 |
| Jacobson Investments Ltd | Real estate | 2021 |
| Jadesa Court Management (New Barnet) Limited | Households | 1973 |
| Jaegerson Digital Limited | Information & communication | 2013 |
| Jaffna Stallions Ltd | Education | 2020 |
| JAG Real Estate Consultants Ltd | Professional & scientific | 2022 |
| Jaks Harrow Ltd | Real estate | 2019 |
| Jalaram Constructions UK Limited | Construction | 2020 |
| Jamdan Ltd | Information & communication | 2019 |
| James 2021 Limited | Real estate | 2021 |
| James Ashley Gutter Cleaning Ltd | Administrative & support | 2025 |
| James Asset Management Limited | Financial services | 2025 |
| James Bakes Ltd | Manufacturing | 2025 |
| James Carpentry & Furniture Limited | Construction | 2013 |
| James Chapman Research Ltd | Professional & scientific | 2017 |
| James Creative Design Ltd | Construction | 2012 |
| James Holdings Sussex Limited | Financial services | 2026 |
| James Pitchley Ltd | Extraterritorial | 2014 |
| James Rayani FI LLP | | 2022 |
| James Saba Limited | Real estate | 2006 |
| James Windsor Design Ltd | Other services | 2011 |
| Jamjar Solutions Limited | Information & communication | 2018 |
| Jand Holdings Limited | Real estate | 2020 |
| Jandra Ltd | Real estate | 2011 |
| Jane Davis Properties Limited | Real estate | 2016 |
| Jane Dutton Communications Limited | Professional & scientific | 2012 |
| Japan Trade Co. Ltd | Wholesale & retail | 2022 |
| Jardonmacher Holdings Limited | Financial services | 2018 |
| Jarvis Training Management Limited | Education | 1989 |
| JAS Cleaners Ltd | Administrative & support | 2008 |
| Jasmin Express Limited | Other services | 2018 |
| Jasmin PVT Limited | Wholesale & retail | 2025 |
| Jasmina Vico Limited | Health & social care | 2019 |
| Jasmina Vico Skin Ltd. | Other services | 2015 |
| Jason Chalk & Sons Limited | Administrative & support | 2019 |
| Jason Faichney Consultancy Limited | Information & communication | 2007 |
| Jason Hamrouni Properties Ltd | Real estate | 2020 |
| Jason Oliver Properties Limited | Real estate | 2009 |
| Jason Silver Limited | Arts & recreation | 2014 |
| Jaspa (Finchley) Ltd | Hospitality | 2024 |
| Jaspa Barnet (UK) Ltd | Hospitality | 2011 |
| Jaspa Edmonton Ltd | Hospitality | 2009 |
| Jaspa Group Ltd | Hospitality | 2021 |
| Jaspa Group Property Limited | Real estate | 2021 |
| Jaspa Lakeside Ltd | Administrative & support | 2024 |
| Jasti Property Solutions Ltd | Real estate | 2020 |
| JAT Properties Ltd | Real estate | 2013 |
| Jauncey Programming Services Ltd | Information & communication | 2014 |
| JAV Holdings Limited | Hospitality | 2025 |
| JAV Locums Limited | Health & social care | 2013 |
| Java Go Ltd | Wholesale & retail | 2022 |
| Javesd Limited | Professional & scientific | 2019 |
| JAW Management Agency Ltd | Professional & scientific | 2020 |
| JAY Consulting Systems Ltd | Health & social care | 2016 |
| Jazz Feet Ltd | Health & social care | 2016 |
| JB BTL Ltd | Real estate | 2022 |
| JB Construction (Barnet) Ltd | Construction | 2018 |
| JBD Electrical Ltd | Construction | 2025 |
| JBD Mixed Media Limited | Professional & scientific | 2018 |
| JBT Security Limited | Manufacturing | 2020 |
| JC Carpentry (London) Limited | Construction | 2015 |
| JC Garden Maintenance Services Ltd | Administrative & support | 2025 |
| Jcnl Limited | Financial services | 2021 |
| Jcs-Oz Ltd | Administrative & support | 2014 |
| Jcsm Holdings Ltd | Financial services | 2024 |
| JD Residential Developments Ltd | Construction | 2020 |
| JD. Building Services (London) Limited | Construction | 2017 |
| JDH Properties Limited | Financial services | 2016 |
| Jdjj Properties Limited | Construction | 2013 |
| Jdunn Holdings Limited | Financial services | 2025 |
| Jean Bernard Paul Ltd | Extraterritorial | 2025 |
| Jech Investments Limited | Financial services | 2023 |
| Jedamo Ltd | Professional & scientific | 2021 |
| Jeffy Restaurant Ltd | Hospitality | 2024 |
| Jelks England Limited | Manufacturing | 2019 |
| Jeloto Investments Limited | Administrative & support | 2005 |
| Jenadco Limited | Professional & scientific | 2000 |
| Jenchenne SRL Limited | Wholesale & retail | 2025 |
| Jengers Mead Car Park Holdings Ltd | Transport & logistics | 2020 |
| Jenica Limited | Wholesale & retail | 2013 |
| JES Electrical SVS Ltd | Construction | 2025 |
| Jess Stebbings Styling Ltd | Professional & scientific | 2012 |
| Jessb Ltd | Real estate | 2025 |
| Jessica Kanerva Ltd | Hospitality | 2020 |
| Jetseal Limited | Wholesale & retail | 1989 |