| JAM Shenfield Limited | Real estate | 2023 |
| James & Sons Construction Limited | Construction | 2005 |
| James and Sons Property Ltd | Real estate | 2024 |
| James Beagle Consultancy Ltd | Other services | 2015 |
| James Chalmers Limited | Wholesale & retail | 1998 |
| James Cliff Consulting Limited | Professional & scientific | 2011 |
| James Hennessy Limited | Construction | 2022 |
| James Scade Golf Limited | Other services | 2020 |
| Jamesons Mechanical Services Ltd | Construction | 2024 |
| Jandu Basildon Services Ltd | Wholesale & retail | 2022 |
| Jannah Funeral Trust UK Limited | Extraterritorial | 2020 |
| Janton Building and Double Glazing Limited | Construction | 1979 |
| Janus Concierge Services Ltd | Professional & scientific | 2018 |
| Japanese Rice Shop Ltd | Wholesale & retail | 2023 |
| Japh Nyakz Services Ltd | Administrative & support | 2024 |
| Jarmar Ltd | Construction | 2017 |
| Jason Consulting Limited | Health & social care | 2015 |
| Jassar Properties Limited | Real estate | 2025 |
| Jaxx Engineering Consultancy Ltd | Professional & scientific | 2023 |
| JAY Events Ltd | Information & communication | 2025 |
| Jayawor IT Services Limited | Information & communication | 2017 |
| Jayvees Limited | Real estate | 2023 |
| Jaywick Commercial Energy and Trade LLP | | 2026 |
| JB Protec Roofing Ltd | Construction | 2023 |
| JB Services (Installations) Limited | Administrative & support | 2004 |
| JBC Windows Ltd | Construction | 2025 |
| Jbdb Holdings Limited | Financial services | 2025 |
| JBK Electrical Limited | Construction | 2011 |
| JBR Ceilings Limited | Construction | 2024 |
| JBR Flooring Limited | Construction | 2025 |
| JBS Equipment Limited | Administrative & support | 2012 |
| JC Cooling Services Limited | Construction | 2026 |
| JC Glazing Improvements Limited | Construction | 2023 |
| JCC Care Limited | Health & social care | 2013 |
| Jcch Property Management Ltd | Real estate | 2020 |
| JCH Technical Services Ltd | Construction | 2012 |
| JCJ Cleaning Services Limited | Administrative & support | 2014 |
| Jcjewelry Limited | Wholesale & retail | 2025 |
| JCM Contracts (Essex) Limited | Construction | 2016 |
| JCM Supplies Ltd | Administrative & support | 2013 |
| JCN Flooring Ltd | Construction | 2018 |
| JCS Building & Maintenance Ltd | Construction | 2015 |
| JCW Lifts Ltd | Manufacturing | 2015 |
| JD Retail Ltd | Wholesale & retail | 2024 |
| Jdavis Mechanical Limited | Construction | 2024 |
| JDH TM Limited | Construction | 2025 |
| JDR Design Ltd | Professional & scientific | 2021 |
| JDS Aviation Services Ltd | Manufacturing | 2017 |
| JDS Plumbing Ltd | Construction | 2019 |
| JDY Consultancy Limited | Other services | 2019 |
| Jeakins Removals Limited | Transport & logistics | 1981 |
| Jecacok Ltd | Wholesale & retail | 2025 |
| Jecco Limited | Real estate | 2014 |
| Jeckles,Boo,Dodger & Co Ltd | Administrative & support | 2018 |
| Jedkiss Limited | Administrative & support | 2013 |
| Jedrem Consulting Ltd | Professional & scientific | 2016 |
| Jeffries Family Company Limited | Financial services | 2014 |
| Jehoel Ltd | Real estate | 2023 |
| Jellyfish Coatings Limited | Construction | 2007 |
| JEM Training Limited | Education | 2014 |
| Jemkam Properties Ltd | Real estate | 2024 |
| Jemmys Catering Ltd | Hospitality | 2011 |
| Jenita Ltd | Wholesale & retail | 2024 |
| Jennings Renovations Ltd | Water & waste | 2021 |
| Jenno's 8 Pipework & Plumbing Limited | Construction | 2011 |
| Jenny M Limited | Other services | 2023 |
| Jeno International Ltd Ltd | Wholesale & retail | 2024 |
| Jerk and Chips Ltd | Hospitality | 2026 |
| Jerked Limited | Other services | 2023 |
| JES Afro-Caribbean Food Market Limited | Wholesale & retail | 2015 |
| JES Hair & Cosmetic World Limited | Other services | 2015 |
| JES Property Investments Limited | Real estate | 2025 |
| JES Stores Limited | Wholesale & retail | 2021 |
| Jesa Systems Limited | Information & communication | 2016 |
| Jeshiens Hair & Beauty Supply Ltd | Other services | 2023 |
| Jess Foresight Healthcare Limited | Public administration | 2021 |
| Jessica Elizabeth Photography Limited | Professional & scientific | 2020 |
| Jessica Hurrell Interiors Limited | Construction | 2023 |
| Jessica Nails Spa Ltd | Other services | 2020 |
| Jessica Rose Comms Ltd | Professional & scientific | 2025 |
| Jesus Liberation Ministry | Education | 2019 |
| JET Brothers Limited | Administrative & support | 2023 |
| JET9 London Limited | Transport & logistics | 2025 |
| Jetform Services Limited | Construction | 1992 |
| Jetstream Technology Solutions Ltd | Information & communication | 2019 |
| Jewelbatch Limited | Other services | 1992 |
| Jewills Holdings Limited | Real estate | 2025 |
| Jewills Limited | Construction | 2022 |
| JEZ Auto's Limited | Wholesale & retail | 2025 |
| JEZ Dickson Creative Ltd | Professional & scientific | 2011 |
| JF Steel Reinforcement Limited | Construction | 2013 |
| JFT Scaffolding Ltd | Construction | 2019 |
| JFW Consulting Limited | Professional & scientific | 2025 |
| JG Fire Systems Ltd | Construction | 2026 |
| JGS Fire Safety Ltd | Public administration | 2016 |
| JH Cloud Solutions Ltd | Information & communication | 2025 |
| JH Safety Solutions Limited | Construction | 2018 |
| Jhalawan Trading Ltd | Wholesale & retail | 2026 |
| Jhoner Health Staffing Ltd | Health & social care | 2014 |
| JHR Personal Training Limited | Health & social care | 2024 |