| J Swait & Sons Limited | Real estate | 2016 |
| J T T Autotech Limited | Wholesale & retail | 2001 |
| J V V Investments Ltd | Financial services | 2021 |
| J Ward Properties Ltd | Households | 2017 |
| J White Plumbing & Building Ltd | Construction | 2002 |
| J. R. T. & Company (Investments) Limited | Real estate | 1979 |
| J. Smith & Sons Schoolwear Limited | Administrative & support | 2004 |
| J.E.G. Properties Limited | Real estate | 2013 |
| J.O & a JAY Investments Limited | Real estate | 2021 |
| Jaaf Trading Ltd | Manufacturing | 2021 |
| JAB Projects Ltd | Wholesale & retail | 2019 |
| Jaba Music Ltd | Information & communication | 2007 |
| Jack Till Logistics Limited | Transport & logistics | 2015 |
| Jackie Blackman Limited | Administrative & support | 2008 |
| Jackpot Group Limited | Real estate | 2018 |
| Jakin Limited | Financial services | 2008 |
| Jakomak Limited | Extraterritorial | 2009 |
| James & Rachel Youngman Properties Ltd | Real estate | 2025 |
| James Jones Music Ltd | Arts & recreation | 2023 |
| James Youngman Private Practice Ltd | Health & social care | 2025 |
| Jamie Catto Mentoring Ltd | Education | 2014 |
| Jamie Catto Music Ltd | Arts & recreation | 2014 |
| Jarvis RE Limited | Construction | 2023 |
| Jask Investments Limited | Financial services | 2018 |
| Jasmine Thai Kitchen Ltd | Hospitality | 2024 |
| Javalon Estates LLP | | 2011 |
| Jaxors Limited | Professional & scientific | 2023 |
| JAY Coleman Lighting and Electrical Solutions Ltd | Construction | 2025 |
| Jaysen Limited | Information & communication | 2021 |
| JB Drywall Consultants Limited | Construction | 2025 |
| Jbsa Estates Limited | Real estate | 2019 |
| Jbsa Solutions Limited | Information & communication | 2011 |
| Jcb-Universal Specialist Care Services Ltd | Public administration | 2021 |
| JCE Estates Ltd | Administrative & support | 2023 |
| JCM Business Ltd | Construction | 2014 |
| JD Car Wash Ltd | Wholesale & retail | 2022 |
| Jdmartin Kitchens Ltd | Construction | 2024 |
| Jdmartinuk Limited | Construction | 2016 |
| Jeekab Investments Ltd | Real estate | 2016 |
| Jeekab Limited | Administrative & support | 2012 |
| Jeff Barnes International Limited | Professional & scientific | 1996 |
| JET Financial Services Ltd | Financial services | 2019 |
| JFM Capital Limited | Financial services | 2025 |
| JG Consultancies Ltd | Financial services | 2015 |
| JG Resi Ltd | Construction | 2021 |
| JGH Property Holdings Limited | Construction | 2025 |
| Jgpc Limited | Hospitality | 2016 |
| JGS Music Limited | Information & communication | 2003 |
| Jgwy Limited | Construction | 2022 |
| JH Baban Holdings Ltd | Real estate | 2024 |
| JHJ Construction Ltd | Construction | 2019 |
| Jhpb Services UK Limited | Wholesale & retail | 2017 |
| Jhugroo Limited | Professional & scientific | 2018 |
| Jiabao Trading Limited | Wholesale & retail | 2025 |
| Jigisha Patel Research Integrity Limited | Professional & scientific | 2022 |
| Jigsaw Consultants Limited | Administrative & support | 1993 |
| JJ Auto Solutions Limited | Wholesale & retail | 2014 |
| JJ Masani Properties Limited | Real estate | 2025 |
| JJ MEN Builders Ltd | Construction | 2023 |
| JJ Multitrade Property Maintenance Limited | Construction | 2025 |
| Jjsd Properties Limited | Real estate | 2022 |
| JK Venetian Plaster Ltd | Construction | 2026 |
| JKS Property Developments Limited | Real estate | 2011 |
| Jldeeks Ltd | Professional & scientific | 2021 |
| JLJ Capital Limited | Real estate | 2020 |
| JM Intermediaries Limited | Information & communication | 2013 |
| JM Success Ltd | Financial services | 2011 |
| JMD Surveying Limited | Professional & scientific | 2014 |
| JMJ Advisory Group Limited | Financial services | 2024 |
| JMJ Healthcare & Environmental Consultancy Limited | Health & social care | 2021 |
| JMJ Property Group Limited | Real estate | 2017 |
| Jmktemi Limited | Professional & scientific | 2019 |
| JOB Lots (London) Ltd | Wholesale & retail | 2025 |
| Jodi Trade Limited | Extraterritorial | 2023 |
| JOE Miller L.D.C. Limited | Other services | 2011 |
| Joert Property Ltd | Real estate | 2025 |
| John Alexander Limited | Professional & scientific | 1996 |
| John Alexander Management Services Limited | Extraterritorial | 1989 |
| John Grants (Estate Agents) Limited | Real estate | 1999 |
| John Grants Management Ltd | Households | 2020 |
| John Ruben Ltd | Construction | 2015 |
| Johri Traders Ltd | Wholesale & retail | 2021 |
| Joint Production System Ltd | Professional & scientific | 2014 |
| JON Stone Entertainment Limited | Arts & recreation | 2020 |
| Jonathan Clark Architects Limited | Professional & scientific | 2013 |
| Jones & Sons Roofing Limited | Construction | 2012 |
| Jones Signs Limited | Manufacturing | 2013 |
| Jones Skip Hire Limited | Water & waste | 2008 |
| Jordan Thomas Music Limited | Arts & recreation | 2016 |
| JOT Property Investments Limited | Financial services | 2020 |
| JP Property Investment Solutions Limited | Real estate | 2019 |
| JPJ Law Ltd | Professional & scientific | 2023 |
| JPS Scaffolding Solutions Ltd | Construction | 2016 |
| JPS Site Solutions Ltd | Administrative & support | 2025 |
| JPY Optical Ltd | Health & social care | 2025 |
| JR Construction & Consultancy Services Ltd | Construction | 2023 |
| JR Larner Limited | Other services | 2025 |
| JRH Imports Limited | Wholesale & retail | 2000 |
| Jrpp Services Limited | Administrative & support | 2020 |
| Jrrp Limited | Real estate | 2025 |