| JET Realisations Limited | | 1971 |
| Jetlets Limited | Real estate | 2019 |
| Jetstream Equity Limited | Financial services | 2007 |
| Jewel Financial Holdings Limited | Financial services | 2016 |
| JF Property Holdings Limited | Construction | 2022 |
| JFP Limited | Wholesale & retail | 2015 |
| JG AV Services Ltd | Information & communication | 2022 |
| JG Crest Enterprises Limited | Information & communication | 2025 |
| JGC Flowtec Ltd | Professional & scientific | 2018 |
| Jgprecruitment Ltd. | Administrative & support | 2022 |
| JGT Legal Consultants Limited | Professional & scientific | 2016 |
| JGT Technical Services Limited | Construction | 2025 |
| JH Professional Consultancy Services Ltd | Professional & scientific | 2024 |
| Jhts Engineering Ltd | Education | 2024 |
| JIB & SON BTL Ltd | Real estate | 2025 |
| Jimmeeco Ltd | Transport & logistics | 2025 |
| Jimrik Ltd | Construction | 2025 |
| Jiyatech Limited | Information & communication | 2019 |
| JJ Books Ltd | Information & communication | 2020 |
| JJ Estore Ltd | Wholesale & retail | 2021 |
| Jkdw Consulting Ltd | Information & communication | 2023 |
| JKG Autos Ltd | Wholesale & retail | 2017 |
| JKG Camper Van Hire Ltd | Administrative & support | 2025 |
| Jkgupta Trading Ltd | Transport & logistics | 2013 |
| JKM Project Management Limited | Professional & scientific | 2023 |
| Jkmp Engineering Limited | Construction | 2024 |
| JKO Building Company Ltd | Construction | 2024 |
| JL Plumbing and Bathrooms Services Limited | Construction | 2022 |
| JL Plumbing and Heating Services Limited | Construction | 2026 |
| JLK Media Ltd | Professional & scientific | 2025 |
| JLS Construction & Groundworks Ltd | Construction | 2024 |
| JM Media Solutions Limited | Administrative & support | 2013 |
| JM24 Healthcare Ltd | Health & social care | 2021 |
| Jmaholm Limited | Health & social care | 2016 |
| Jmcl Freightways Limited | Transport & logistics | 2015 |
| Jmkz Ltd | Administrative & support | 2024 |
| JN & Son's Properties Ltd | Real estate | 2025 |
| JN Fencing & Landscaping Ltd | Administrative & support | 2021 |
| Jnest Ltd | Information & communication | 2025 |
| Jnest Properties Ltd | Real estate | 2025 |
| JNJ Cars Ltd | Transport & logistics | 2018 |
| JNP Foods Ltd | Wholesale & retail | 2010 |
| JO Cherry Training Limited | Administrative & support | 2008 |
| Jo&Bo Ltd | Transport & logistics | 2011 |
| Joanna Opiat-Iwan Ltd | Public administration | 2023 |
| JOC Sports Therapies Ltd | Health & social care | 2020 |
| Jocoserious Finance Ltd | Professional & scientific | 2023 |
| JOE Allnutt Osteopathy Limited | Health & social care | 2025 |
| JOE Drive Ltd | Transport & logistics | 2018 |
| JOE Newman Media Limited | Wholesale & retail | 2020 |
| Joes Kebabs Limited | Hospitality | 2013 |
| John M.Carter,Limited | Manufacturing | 1934 |
| John S Cargo Ltd | Transport & logistics | 2024 |
| Joint Funding Solutions Ltd | Financial services | 2006 |
| Joje Ltd | Wholesale & retail | 2020 |
| Jomo Ventures Ltd | Professional & scientific | 2023 |
| Jonathan Williams Independent Funeral Directors Ltd | Other services | 2019 |
| Jonnick Ltd | Real estate | 2025 |
| Jonp Limited | Information & communication | 2016 |
| Jonsson Consulting Limited | Professional & scientific | 2008 |
| Jose Fish and Chips Limited | Hospitality | 2022 |
| Josef Consultancy Ltd | Administrative & support | 2024 |
| Josh Treatments Ltd | Other services | 2025 |
| JOURNEY11 Technologies Limited | Information & communication | 2015 |
| Joyce Holdings Limited | Financial services | 2019 |
| Joyce Swimming Pools Limited | Construction | 2013 |
| Jozhu Ltd | Wholesale & retail | 2024 |
| JP Heritage Ltd | Professional & scientific | 2019 |
| JP Innovate Ltd | Information & communication | 2025 |
| JP Property Services London Limited | Construction | 2012 |
| JP Training Ltd | Education | 2022 |
| JPA Wheeler Properties Limited | Real estate | 2021 |
| Jpds Trading Ltd | Wholesale & retail | 2025 |
| JPE Foundry Ltd | Information & communication | 2026 |
| Jped Photography Ltd | Professional & scientific | 2026 |
| JPH Renewables Ltd | Construction | 2024 |
| JPM Roofing Solutions Ltd | Construction | 2025 |
| JPW Properties Ltd | Construction | 2018 |
| JR Revit & CAD Innovations Ltd | Information & communication | 2025 |
| Jrkd Care Services Limited | Health & social care | 2017 |
| Jrpes Limited | Professional & scientific | 2025 |
| JS Gourmet Ltd | Manufacturing | 2025 |
| Jsfpropertyuk Limited | Real estate | 2023 |
| JSM Ridler Ltd | Real estate | 2020 |
| JSR Practices Ltd | Health & social care | 2020 |
| JSW (Hampshire) Limited | Real estate | 2019 |
| JT Manor Estates Ltd | Real estate | 2022 |
| JTL Gardening Services Ltd | Administrative & support | 2023 |
| JTS Business Limited | Administrative & support | 2025 |
| Jtys Consulting Limited | Information & communication | 2018 |
| JTZ Limited | Information & communication | 2012 |
| Jube Investments Limited | Real estate | 2016 |
| Jube Services Limited | Real estate | 2016 |
| Judy Wilkes Services Ltd | Professional & scientific | 2012 |
| Jugawana Ltd | Health & social care | 2024 |
| Jugnu Traders Ltd | Wholesale & retail | 2024 |
| June Drive (Basingstoke) Management Company Limited | Households | 2004 |
| Juniper Research Limited | Professional & scientific | 2002 |
| Juniper Smile Studios Ltd | Health & social care | 2024 |
| Juniper Tree Holding Company Limited | Real estate | 2024 |