| ITD Media Ltd | Professional & scientific | 2023 |
| ITE Engineering Services Limited | Professional & scientific | 2008 |
| Ivaana Limited | Health & social care | 2018 |
| J & C Barstow Limited | Construction | 2006 |
| J & G Medical Services Limited | Health & social care | 2022 |
| J & J Bugden & Sons Limited | Agriculture & fishing | 2022 |
| J & LR Limited | Health & social care | 2019 |
| J Brady Consulting Limited | Professional & scientific | 2021 |
| J Grundy Orthopaedics Limited | Health & social care | 2011 |
| J K C Information Technology Limited | Information & communication | 1998 |
| J L Professional Ltd | Arts & recreation | 2012 |
| J R Baker Construction Ltd | Construction | 2013 |
| J R Baker Properties Ltd | Real estate | 2025 |
| J Taylor Build Ltd | Construction | 2022 |
| J W Vehicle Solutions Ltd | Professional & scientific | 2024 |
| J'Toye Digital Ltd | Information & communication | 2025 |
| J.S Woodsmith Limited | Manufacturing | 2019 |
| JAC Medical Services Limited | Health & social care | 2011 |
| Jack Chartering Ltd | Transport & logistics | 2017 |
| Jade House (Romsey) Ltd | Hospitality | 2023 |
| James Court (Management) Limited | Households | 1967 |
| James Fraser Building Services Limited | Construction | 2021 |
| James FRY Associates Limited | Professional & scientific | 2004 |
| James Portfolio Investments Ltd | Real estate | 2023 |
| Japanese Knotweed and Invasive Species Ltd | Administrative & support | 2021 |
| Japanese Knotweed and Invasive Weeds Ltd | Administrative & support | 2021 |
| Jarunet Limited | Health & social care | 2016 |
| Jason Harvey Medicolegal Limited | Health & social care | 2024 |
| JAY Self Limited | Health & social care | 2015 |
| Jays Fm(Eng) Services Ltd | Construction | 2013 |
| JB Containers Limited | Other services | 2021 |
| JB Motor Company (South) Limited | Wholesale & retail | 2016 |
| JBA Project Services Ltd | Professional & scientific | 2025 |
| JD Workshop Ltd | Wholesale & retail | 2021 |
| Jeemed Limited | Health & social care | 2012 |
| Jeff Clark Agencies Limited | Wholesale & retail | 2008 |
| Jellijon Ltd | Manufacturing | 2026 |
| Jemon Sieff Limited | Professional & scientific | 2009 |
| Jennie Maizels Limited | Arts & recreation | 2009 |
| Jerram Surlis Limited | Extraterritorial | 2011 |
| Jeska Limited | Real estate | 2017 |
| Jess Peters Limited | Information & communication | 2024 |
| JH Hippodrome Limited | Professional & scientific | 2021 |
| JHC Recruitment Ltd | Administrative & support | 2017 |
| JHN Holdings Limited | Financial services | 2024 |
| Jigsaw Early Years Academy Ltd | Education | 2022 |
| Jigsaw Early Years Training Ltd | Education | 2026 |
| JJS Anaesthesia Limited | Health & social care | 2021 |
| JJS Building & Carpentry Ltd | Manufacturing | 2020 |
| JJS Property Investments Limited | Real estate | 2025 |
| Jjse Property Services Limited | Real estate | 2024 |
| JK Electrical & Data UK Ltd | Construction | 2020 |
| JKC Video Conferencing Limited | Information & communication | 2005 |
| JL Electrical Controls Ltd | Construction | 2022 |
| JLB Surgery Limited | Health & social care | 2018 |
| JLG Maintenance Ltd | Administrative & support | 2025 |
| Jlmm Healthcare Ltd | Health & social care | 2024 |
| Jmonslowanaesthesia Ltd | Health & social care | 2022 |
| Jmst Property Ltd | Hospitality | 2023 |
| Jnsp Developments Ltd | Real estate | 2024 |
| Jocomotion Limited | Professional & scientific | 2024 |
| JOE Keeps Limited | Professional & scientific | 2025 |
| Joerg Philipp Properties Ltd | Real estate | 2013 |
| Jogai Limited | Professional & scientific | 2015 |
| Johnsen Optical Limited | Health & social care | 2007 |
| Jorgensen Holdings Limited | Financial services | 2024 |
| Jorgensen Limited | Construction | 1990 |
| Joseph Pike Limited | Hospitality | 2025 |
| Joshabi Ventures Ltd | Real estate | 2026 |
| Journey's END Furniture Company Limited | Manufacturing | 2002 |
| Journey's END Interiors Limited | Wholesale & retail | 2023 |
| Journeyman Carpentry Limited | Construction | 2017 |
| Joyners Limited | Real estate | 2012 |
| JPC Technologies Ltd | Construction | 2018 |
| JPL Investments Limited | Real estate | 2020 |
| JRT Products Ltd | Wholesale & retail | 2024 |
| JSB Global Limited | Professional & scientific | 2017 |
| JSK Surgery Limited | Health & social care | 2018 |
| Judd Stewart Medical Consultancy Limited | Health & social care | 2025 |
| Jupiter Capital Ltd | Administrative & support | 2012 |
| Just 4 Funk Productions Limited | Arts & recreation | 2009 |
| Just Communications Ltd | Professional & scientific | 2021 |
| Just Go Holdings Limited | Financial services | 2026 |
| Just Grooming Ltd | Education | 2019 |
| Just SEW Romsey Ltd | Other services | 2021 |
| Justfloors Limited | Construction | 1993 |
| Jv-Crypto Ltd | Information & communication | 2019 |
| JVM Auto Ltd | Wholesale & retail | 2021 |
| JVT Recruitment Limited | Administrative & support | 2012 |
| K and a Capital Ltd | Real estate | 2023 |
| Kado Cafe Limited | Hospitality | 2023 |
| Kala Chethena Kathakali Troupe | Arts & recreation | 1994 |
| KAR & Poddar Associates Limited | Health & social care | 2021 |
| Karma Couriers Limited | Transport & logistics | 2019 |
| KARMA2DHARMA Ltd | Professional & scientific | 2025 |
| Karsian Limited | Health & social care | 2019 |
| Kauri Medical Limited | Health & social care | 2022 |
| KB QA Limited | Professional & scientific | 2011 |
| Kebumo Limited | Hospitality | 2024 |
| Keep Stub Limited | Manufacturing | 2025 |